全文获取类型
收费全文 | 6100篇 |
免费 | 295篇 |
国内免费 | 7篇 |
出版年
2022年 | 14篇 |
2021年 | 60篇 |
2020年 | 32篇 |
2019年 | 51篇 |
2018年 | 91篇 |
2017年 | 61篇 |
2016年 | 126篇 |
2015年 | 173篇 |
2014年 | 206篇 |
2013年 | 533篇 |
2012年 | 362篇 |
2011年 | 384篇 |
2010年 | 232篇 |
2009年 | 240篇 |
2008年 | 393篇 |
2007年 | 416篇 |
2006年 | 374篇 |
2005年 | 412篇 |
2004年 | 396篇 |
2003年 | 416篇 |
2002年 | 333篇 |
2001年 | 61篇 |
2000年 | 37篇 |
1999年 | 72篇 |
1998年 | 87篇 |
1997年 | 73篇 |
1996年 | 60篇 |
1995年 | 54篇 |
1994年 | 57篇 |
1993年 | 60篇 |
1992年 | 46篇 |
1991年 | 36篇 |
1990年 | 36篇 |
1989年 | 24篇 |
1988年 | 28篇 |
1987年 | 15篇 |
1986年 | 20篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 31篇 |
1981年 | 48篇 |
1980年 | 28篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1974年 | 10篇 |
1973年 | 13篇 |
排序方式: 共有6402条查询结果,搜索用时 31 毫秒
51.
Toshinori Nagaoka Ken-ichi Umezu Kenji Kouno Satoshi Yoshida Yukio Ishiguro Tadao Ando 《Plant Growth Regulation》1996,20(3):295-302
Water extracts of the compost produced from activated sludge and coffee residue were found to be selectively inhibitory to seed germination of some legumes. Germination rate of white clover (Trifolium repens L.), red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) seeds were reduced to 2, 29 and 73% of the control, respectively, by water extracts of the compost (20 g l–1). However, the extracts did not show any inhibition to seed germination of sorghum (Sorghum bicolor Moench), African millet (Eleusine coracana Gaertn.), and Komatsuna (Brassica rapa L.) at the same concentration. The inhibitors in the compost extracts were separated by ion-exchange chromatography and reverse-phase high performance liquid chromatography (HPLC) and the inhibitory activities of seed germination were tested with white clover seeds. Five inhibitors were isolated and identified as 3,4-dichlorophenylacetic acid (3,4-DCP), 3,4-dichlorobenzoic acid (3,4-DCB), 3,4,5-trichlorophenylacetic acid, 3,4,5-trichlorobenzoic acid and mono-2-ethylhexylphthalate by 1H-, 13C-NMR spectroscopy and mass spectrometry. The inhibitory activities of some authentic chemicals of the inhibitors and the related compounds were compared. The results indicated that the main inhibitor in the compost could be 3,4-DCB, which was contained at the concentration of 6.58 mg kg–1 compost and showed the strongest inhibitory effect on seed germination of white clover among the tested compounds. 相似文献
52.
In rodents an intravenous administration of viableCryptococcus (C.) neoformans cells frequently resulted in attachment of intravascular cryptococcal granulomas to inner walls of the large to medium-sized
veins of various organs, including the lungs, liver and spleen. In order to elucidate the pathogenesis of granulomatous changes,
the cells composing the intravascular granulomas were observed by electron microscopic peroxidase (PO) cytochemistry. The
granuloma composing cells could be divided into the following four types according to the pattern of endogenous peroxidase
activity: exudate macrophage (Mφ, type I), PO-negative Mφ (type II), resident Mφ (type III) and other inflammatory cells (type
IV). In the intravenous granulomas of the lung, the percentages of composed cells were 39.0% for type I, 57.9% for type II,
0% for type III and 3.1% for type IV. By contrast, in the interstitial granulomas in the lung, type III Mφs, possibly derived
from alveolar Mφs, played a significant role in granuloma formation. This may indicate that the intravascular granuloma is
almost composed of macrophages derived from monocytes rather than alveolar macrophages. The expression of ICAM-1 on endothelia
of the pulmonary veins was examined by immunoelectron microscopy. An immunogold labeling index was significantly augmented
on the surface of endothelia in response to intravenous challenge ofC. neoformans. The intravascular granuloma demonstrates that the monocytes develop into the granuloma-composing macrophages and suppress
the cryptococcal activities even hi the peripheral blood resulting in an assistance of endothelial functions. 相似文献
53.
Isolation of a gene essential for biosynthesis of the lipopeptide antibiotics plipastatin B1 and surfactin in Bacillus subtilis YB8 总被引:12,自引:0,他引:12
Bacillus subtilis YB8 was found to produce the lipopeptide antibiotics surfactin and plipastatin B1. A gene, lpa-8, required for the production of both lipopeptides was cloned from strain YB8. When this gene was inactivated in strain YB8,
neither surfactin nor plipastatin B1 was produced. However, the defective strain transformed with an intact lpa-8 gene had restored ability to produce both peptides. Nucleotide sequence analysis of the region essential for the production
of the peptides revealed the presence of a large open reading frame. The deduced amino acid sequence of lpa-8 (224 amino acid residues) showed sequence similarity to that of sfp (from surfactin-producing B. subtilis), lpa-14 (from iturin A- and surfactin-producing B. subtilis), psf-1 (from surfactin-producing Bacillus pumilus), gsp (from gramicidin-S-producing Bacillus brevis), and entD (from siderophore-enterobactin-producing Escherichia coli), which are able to complement a defect in the sfp gene and promote production of the lipopeptide antibiotic surfactin. The sequence similarity among these proteins and the
product similarity of cyclic peptides suggests that they might be involved in the biosynthesis or secretion of the peptides.
Received: 14 July 1995 / Accepted: 22 December 1995 相似文献
54.
Kenji Kondo Susumu Terabayashi Minoru Okada Changqi Yuan Shanan He 《Journal of plant research》1996,109(1):21-27
Cnidium officinale Makino is important medicinally and economically, but its origin is uncertain. The phylogenetic relationship ofC. officinale is provided from the analyses based on the ribulose-1,5-bisphosphate carboxylase/oxgenase gene (rbcL) sequences of 41 species which represent the 34 genera of Aplaceae, the four genera of Araliaceae, and one genus each of
Pittosporaceae, Cornaceae, and Caprifoliaceae. The strict consensus tree obtained supports a close relationship ofC. officinale to the Chinese members ofLigusticum, especially toL. chuanxiong. Additionally, the tree shows (1) polyphyly of the genusLigusticum and (2) monophyly of the subfamily Apioideae. Within Apioideae, we recognized some groups in our phylogenetic tree. The grouping
is discordant in several respects with the traditional tribal divisions based mainly on fruit morphology. 相似文献
55.
Fine mapping of the Autosomal Dominant Split Hand/Split Foot Locus on Chromosome 7, Band q21.3-q22.1 总被引:6,自引:3,他引:3 下载免费PDF全文
Stephen W. Scherer Parvoneh Poorkaj Todd Allen Julia Kim Dorrit Geshuri Mark Nunes Sylvia Soder Karen Stephens Roberta A. Pagon Michael A. Patton Mary Anne Berg Tim Donlon Horacio Rivera R. A. Pfeiffer Kenji Naritomi Helen Hughes Maurizio Genuardi Fiorella Gurrieri Giovanni Neri Everett Lovrein Ellen Magenis Lap-Chee Tsui James P. Evans 《American journal of human genetics》1994,55(1):12-20
Split hand/split foot (SHFD) is a human developmental defect characterized by missing digits, fusion of remaining digits, and a deep median cleft in the hands and feet. Cytogenetic studies of deletions and translocations associated with this disorder have indicated that an autosomal dominant split hand/split foot locus (gene SHFD1) maps to 7q21-q22. To characterize the SHFD1 locus, somatic cell hybrid lines were constructed from cytogenetically abnormal individuals with SHFD. Molecular analysis resulted in the localization of 93 DNA markers to one of 10 intervals surrounding the SHFD1 locus. The translocation breakpoints in four SHFD patients were encompassed by the smallest region of overlap among the SHFD-associated deletions. The order of DNA markers in the SHFD1 critical region has been defined as PON–D7S812–SHFD1–D7S811–ASNS. One DNA marker, D7S811, detected altered restriction enzyme fragments in three patients with translocations when examined by pulsed-field gel electro-phoresis (PFGE). These data map SHFD1, a gene that is crucial for human limb differentiation, to a small interval in the q21.3-q22.1 region of human chromosome 7. 相似文献
56.
In Vitro Bleaching of Hardwood Kraft Pulp by Extracellular Enzymes Excreted from White Rot Fungi in a Cultivation System Using a Membrane Filter 总被引:6,自引:4,他引:2 下载免费PDF全文
To clarify the role of excreted extracellular enzymes during long-term incubation in a pulp biobleaching system with white rot fungi, we developed a cultivation system in which a membrane filter is used; this membrane filter can prevent direct contact between hyphae and kraft pulp, but allows extracellular enzymes to attack the kraft pulp. Phanerochaete sordida YK-624 brightened the pulp 21.4 points to 54.0% brightness after a 5-day in vitro treatment; this value was significantly higher than the values obtained with Phanerochaete chrysosporium and Coriolus versicolor after a 7-day treatment. Our results indicate that cell-free, membrane-filtered components from the in vitro bleaching system are capable of delignifying unbleached kraft pulp. Obvious candidates for filterable reagents capable of delignifying and bleaching kraft pulp are peroxidase and phenoloxidase proteins. The level of secreted manganese peroxidase activity in the filterable components was substantial during strain YK-624 in vitro bleaching. A positive correlation between the level of manganese peroxidase and brightening of the pulp was observed. 相似文献
57.
Induction of Manganese Superoxide Dismutase by Cytokines and Lipopolysaccharide in Cultured Mouse Astrocytes 总被引:2,自引:1,他引:1
Kenji Mokuno Kunihiko Ohtani Akio Suzumura Kazuhiro Kiyosawa Yoshikiyo Hirose Kuniyuki Kawai †Kanefusa Kato 《Journal of neurochemistry》1994,63(2):612-616
Abstract: To determine whether cytokines or lipopolysaccharide (LPS) are involved in the induction of superoxide dismutase (SOD) in the nervous system, we examined the effects of these substances on the levels of SOD in cultured mouse astrocytes. Treatment of astrocytes with 102 to 104 U/ml tumor necrosis factor-α for 3 days increased the levels of Mn SOD in a dose- and time-dependent manner to as much as six times the level under nontreated conditions. Treatment with 1.0 µg/ml LPS for 3 days elicited a fourfold increase in levels of Mn SOD, and the effect of LPS was also dose dependent. Furthermore, Mn SOD in astrocytes was induced by a 3-day exposure to interleukin-1α at concentrations of 102 or 103 U/ml. However, these stimuli had no effect on levels of copper-zinc SOD (Cu/Zn SOD) in astrocytes. By contrast, interferon-γ did not change the levels of either Mn or Cu/Zn SOD in the cells. The results indicate that the selective induction of Mn SOD by cytokines and LPS, which has been observed in nonnervous tissues, may also occur in nervous tissues. The induction of Mn SOD may represent a mechanism for protection of cells from oxidative stress. 相似文献
58.
Autotrophic picoplankton in southern Lake Baikal: abundance, growth and grazing mortality during summer 总被引:5,自引:0,他引:5
Nagata Toshi; Takai Kenji; Kawanobe Kyoko; Kim Dong-Sup; Nakazato Ryoji; Guselnikova Nina; Bondarenko Nina; Mologawaya Oliga; Kostrnova Tatyana; Drucker Valentine; Satoh Yasuhiro; Watanabe Yasunori 《Journal of plankton research》1994,16(8):945-959
Autotrophic picoplankton were highly abundant during the thermalstratification period in late July in the pelagic area (waterdepth 5001300 m) of southern Lake Baikal; maximum numberswere 2 x 106 cells ml1 in the euphotic zone ({small tilde}15m). Unicellular cyanobacteria generally dominated the picoplanktoncommunity, although unidentified picoplankton that fluorescedred under blue excitation were also abundant (maximum numbers4 x 105 cells ml1) and contributed up to {small tilde}40%of the total autotrophic picoplankton on occasions. Carbon andnitrogen biomasses of autotrophic picoplankton estimated byconversion from biovolumes were 1484 µg C l1and 3.621 µg N l1. These were comparableto or exceeded the biomass of heterotrophic bacteria. Autotropicpicoplankton and bacteria accounted for as much as 33% of paniculateorganic carbon and 81% of nitrogen in the euphotic zone. Measurementsof the photosynthetic uptake of [l4C]bicarbonate and the growthof picoplankton in diluted or size-fractionated waters revealedthat 80% of total primary production was due to picoplankton,and that much of this production was consumed by grazers inthe <20 µ.m cell-size category. These results suggestthat picoplankton-protozoan trophic coupling is important inthe pelagic food web and biogeochemical cycling of Lake Baikalduring summer. 相似文献
59.
Hiromi Maekawa Tomoko Nakagawa Yoko Uno Kenji Kitamura Chikashi Shimoda 《Molecular & general genetics : MGG》1994,244(5):456-464
When the fission yeastSchizosaccharomyces pombe is starved for nitrogen, the cells are arrested in the G1 phase, enter the G0 phase and initiate sexual development. Theste13 mutant, however, fails to undergo a G1 arrest when starved for nitrogen and since this mutant phenotype is not suppressed by a mutation in adenylyl cyclase (cyr1), it would appear thatste13
+ either acts independently of the decrease in the cellular cAMP level induced by starvation for nitrogen, or functions downstream of this controlling event. We have used functional complementation to clone theste13
+ gene from anS. pombe genomic library and show that its disruption is not lethal, indicating that, while the gene is required for sexual development, it is not essential for cell growth. Nucleotide sequencing predicts thatste13
+ should encode a protein of 485 amino acids in which the consensus motifs of ATP-dependent RNA helicases of the DEAD box family are completely conserved. Point mutations introduced into these consensus motifs abolished theste13
+ functions. The predicted Ste13 protein is 72% identical to theDrosophila melanogaster Me31B protein over a stretch of 391 amino acids. ME31B is a developmentally regulated gene that is expressed preferentially in the female germline and may be required for oogenesis. Expression of ME31B cDNA inS. pombe suppresses theste13 mutation. These two evolutionarily conserved genes encoding putative RNA helicases may play a pivotal role in sexual development. 相似文献
60.
We have developed theoretical models for analysis of X-ray diffuse scattering from protein crystals. A series of models are proposed to be used for experimental data with different degrees of precision. First, we propose the normal mode model, where conformational dynamics of a protein is assumed to occur mostly in a limited conformational subspace spanned by a small number of low-frequency normal modes in the protein. When high precision data are available, variances and covariances of the normal mode variables can be determined from experimental data using this model. For experimental data with lower degrees of precision, we introduce a series of simpler models. These models express the covariance matrix using relatively simple empirical correlation functions by assuming the correlation between a pair of atoms to be isotropic. As an application of these simpler models, we calculate diffuse-scattering patterns from a human lysozyme crystal to examine how each adjustable parameter in the models affects general features of the resulting patterns. The results of the calculation are summarized as follows. (1) The higher order scattering makes a significant contribution at high resolutions. (2) The resulting simulated patterns are sensitive to changes in correlation lengths of about 1 Å, as well as to changes of the functional form of the correlation function. (3) But only the “average” value of the intra- and intermolecular correlation lengths seems to determine the gross features of the pattern. (4) The effect of the atom-dependent amplitude of fluctuations is difficult to observe. © 1994 John Wiley & Sons, Inc. 相似文献