全文获取类型
收费全文 | 2224篇 |
免费 | 142篇 |
出版年
2021年 | 16篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 27篇 |
2017年 | 29篇 |
2016年 | 33篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 87篇 |
2012年 | 96篇 |
2011年 | 97篇 |
2010年 | 63篇 |
2009年 | 54篇 |
2008年 | 87篇 |
2007年 | 86篇 |
2006年 | 90篇 |
2005年 | 116篇 |
2004年 | 78篇 |
2003年 | 95篇 |
2002年 | 96篇 |
2001年 | 73篇 |
2000年 | 85篇 |
1999年 | 83篇 |
1998年 | 40篇 |
1997年 | 27篇 |
1996年 | 29篇 |
1995年 | 25篇 |
1994年 | 29篇 |
1993年 | 29篇 |
1992年 | 63篇 |
1991年 | 42篇 |
1990年 | 58篇 |
1989年 | 47篇 |
1988年 | 45篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 29篇 |
1984年 | 34篇 |
1983年 | 14篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 18篇 |
1978年 | 27篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1974年 | 19篇 |
1973年 | 20篇 |
1972年 | 20篇 |
1970年 | 22篇 |
排序方式: 共有2366条查询结果,搜索用时 312 毫秒
991.
Influence of sporulation medium and divalent ions on the heat resistance of Alicyclobacillus acidoterrestris spores 总被引:1,自引:0,他引:1
The influence of divalent cations on the heat resistance of spores of the thermoacidophilic spoilage bacterium Alicyclobacillus acidoterrestris was studied. The heat resistance of A. acidoterrestris spores was not affected by the presence of the different divalent cations (Ca2+ , Mg2+ , Ba2+ , Mn2+ and Sr2+ ) in the sporulation medium, and by the demineralization or remineralization. And the Ca and Mn contents in A. acidoterrestris spores were scarcely changed by these treatments. However, the heat resistance of Bacillus subtilis spores was affected with the changes of Ca content in the spores. The Ca contents in A. acidoterrestris spores of the different forms were greater than the DPA content. In contrast, the DPA content in the B. subtilis spores was greater than the Ca content. These findings suggest that the presence of constant amount of Ca-DPA and a stronger binding characteristic of divalent ions, especially Ca and Mn, is reflected in the specific heat resistance of A. acidoterrestris spores. 相似文献
992.
Hitoshi Ando Nobuhisa Mizuki Masao Ota Masaaki Yamazaki Shigeaki Ohno Kaori Goto Yoshihisa Miyata Kazuo Wakisaka Seiamak Bahram H. Inoko 《Immunogenetics》1997,46(6):499-508
The human major histocompatibility complex (MHC) is located within a 4 megabase segment on chromosome 6p21.3. Recently, a
highly divergent MHC class I chain-related gene family, MIC was identified within the class I region. The MICA and MICB genes in this family have unique patterns of tissue expression. The MICA gene is highly polymorphic, with more than 20 alleles identified to date. To elucidate the extent of MICB allelic variations, we sequenced exons 2 (α1), 3 (α2), 4 (α3), and 5 (transmembrane) as well as introns 2 and 4 of this gene
in 46 HLA homozygous B-cell lines. We report the identification of eleven alleles based on seven non-synonymous, two synonymous, and
four intronic nucleotide variations. Interestingly, one allele has a nonsense mutation resulting in a premature termination
codon in the α2 domain. Thus, MICB appears to have fewer alleles than MICA, not unlike the allelic ratio between the HLA-C and -B loci. A preliminary linkage analysis of the MICB alleles with those of the closely located MICA and HLA-B genes revealed no conspicuous linkage disequilibrium between them, implying the presence of a potential recombination hotspot
between the MICB and MICA genes.
Received: 16 April 1997 / Revised: 19 May 1997 相似文献
993.
Significant R-enantioselection occurred for b-galactosyl transfer to the secondary alcohols, 2-butanol, 2-octanol, 3-methyl-2-butanol, 1-phenylethanol, 1,2-propanediol, 1-methoxy-2-propanol and 3-hydroxybutanoates, with b-galac-tosidase from Escherichia coli. The highest R-enantioselection of 98% e.e. was for the b-galactosylation of 1-phenylethanol using b-galactosidase from E. coli. 相似文献
994.
995.
Tadashi Yamashita Hidetoshi Yamazaki Yasuhiro Kon Tomomasa Watanabe Jiro Arikawa Ichiro Miyoshi Noriyuki Kasai Mikinori Kuwabara 《Free radical biology & medicine》1997,23(7):1073-1077
In the present study we demonstrated the effects of the spin-trapping agent α-phenyl-N-tert-butylnitrone (PBN) on the in vitro development of rat embryos at the early stage. In rat embryos, PBN increased the speed of the first cleavage and had no toxicity during pregnancy after embryo culture. These results showed that reactive oxygen species (ROIs) that were formed by activating molecular oxygens through redox reactions regulated the speed of development for early-stage embryos. Thus, PBN caused a decrease in the level of ROIs and toxicity and an in increase in the level of the development of rat embryos. On the other hand, PBN could not decrease the 2-cell block in vitro nor increase the blastulation rate, in contrast to the fact that a scavenger of superoxide anions, SOD, is effective in doing so for mouse embryos. From these results it was concluded that free radicals play an important role in the in vitro development of rat embryos at the early stage, but play no role in the decrease of the 2-cell block or their blastulation rate. It should be noted that PBN had no toxicity for embryonic development at the 2-cell stage. 相似文献
996.
The teleost dorsoventral axis cannot be distinguished morphologically before gastrulation. In order to examine whether the
yolk cell affects axis determination, we bisect early cleavage embryos of the goldfish, Carassius auratus. When the vegetal yolk hemisphere is removed by bisection along the equatorial plane at the 2-cell stage, the embryos develop
abnormally and exhibit a symmetrical morphology. No dorsal structures, such as notochord, somites and neural tube, differentiate
and no embryonic shield is formed during gastrulation. In addition, no goosecoid mRNA is expressed before gastrulation. The frequency of abnormality decreases as the age at which the vegetal yolk hemisphere
is removed increases. Most embryos removed at the 32-cell stage develop normally. Their morphological phenotype is similar
to that of a Xenopus ventralized embryo generated by ultraviolet irradiation on the vegetal hemisphere soon after fertilization. We also observed
that, when the embryos were bisected along the first cleavage plane at the 2-cell stage, the proportion of pairs of embryos
of which one embryo developed normally was 44.8%. These results indicate that the vegetal yolk hemisphere of the early cleavage
embryo of the goldfish contains axis determination factor(s), which are necessary for generation of dorsal structures. Furthermore,
it is suggested that these determinant(s) are distributed asymmetrically within the vegetal yolk hemisphere.
Received: 25 May 1996 / Accepted: 19 September 1996 相似文献
997.
Hiroyuki Saito Yoshihiro Takahashi Seizaburo Harata Keiko Tanaka Tsuyoshi Sano Tsunehisa Suto Akio Yamada Shudo Yamazaki Morihiro Morita 《Microbiology and immunology》1996,40(4):271-275
In 1993, mumps with a high incidence of aseptic meningitis became prevalent in Akita prefecture, Japan. Three mumps virus isolates obtained from the nonvaccine-associated cases lacked the BamHI restriction cleavage site of the P gene, like the Urabe strain (Yamada, A. et al, Vaccine 8: 553-557). However, four additional nucleotide substitutions were found in the determined region of 157 bp. Fourteen of 19 cases from which mumps virus showing the Urabe-like RFLP profile was detected were complicated with symptomatic meningitis, whereas there were only four cases of meningitis among 23 individuals infected with the wild type showing no Urabe-like RFLP profile (non-“Urabe-like” wild-type). The incidence of meningitis was over 70% among patients infected with the “Urabe-like” wild-type virus. The “Urabe-like” wild-type disappeared after February 1994 in the epidemic area and was replaced by the non-“Urabe-like” wild-type. Patients infected with the “Urabe-like” wild-type lived in a closed colony, in which there were two instances of transmission between siblings. Thus this outbreak was transient and narrowly localized. 相似文献
998.
F. Yamazaki S. Sagawa R. Torii Y. Endo K. Shiraki 《International journal of biometeorology》1997,40(4):200-205
The purpose of this study was to examine the effect of hyperthermia on the carotid baroreceptor-cardiac reflexes in humans.
Nine healthy males underwent acute hyperthermia (esophageal temperature ∼38.0° C) produced by hot water-perfused suits. Beat-to-beat
heart rate (HR) responses were determined during positive and negative R-wave-triggered neck pressure steps from +40 to −65
mm Hg during normothermia and hyperthermia. The carotid baroreceptor-cardiac reflex sensitivity was evaluated from the maximum
slope of the HR response to changes in carotid distending pressure. Buffering capacity of the HR response to carotid distending
pressure was evaluated in % from a reference point calculated as (HR at 0 mm Hg neck pressure−minimum HR)/HR range ×100. An
upward shift of the curve was evident in hyperthermia because HR increased from 57.7±2.4 beats/min in normothermia to 88.7±4.1
beats/min in hyperthermia (P<0.05) without changes in mean arterial pressure. The maximum slope of the curve in hyperthermia was similar to that in normothermia.
The reference point was increased (P<0.05) during hyperthermia. These results suggest that the sensitivity of the carotid baroreflex of HR remains unchanged in
hyperthermia. However, the capacity for tachycardia response to rapid onset of hypotension is reduced and the capacity for
bradycardia response to sudden hypertension is increased during acute hyperthermia.
Received: 14 October 1996 /Revised: 16 January 1997 / Accepted: 21 January 1997 相似文献
999.
AIMS: To devise and evaluate a method for isolating the rare, zoosporic actinomycetes, Actinokineospora spp. in soil and plant litter. METHODS AND RESULTS: The newly developed method consists of two enrichment stages followed by plating on a selective medium. The source material is initially incubated with calcium carbonate to multiply the population of Actinokineospora spp., and is then air-dried. The second stage consists of rehydration-centrifugation, in which the amended substrate is immersed in phosphate buffer-soil extract to liberate actinomycete zoospores, and nonmotile microbial associates are then eliminated by centrifugation. Portions of the supernatant enriched with zoospores are plated on humic-acid vitamin agar supplemented with fradiomycin, kanamycin, nalidixic acid and trimethoprim. We examined 39 soil and plant-litter samples taken from fields, forests and stream banks. The proposed method consistently enriched and selectively isolated Actinokineospora spp. in 17 samples. Evidence for antimicrobial activity was found in most of the isolates. CONCLUSION: A combination of enrichment and a medium containing selective antibiotics can be used successfully for efficient isolation of certain rare actinomycete taxa. SIGNIFICANCE AND IMPACT OF THE STUDY: The development of new methodologies with which to isolate rare actinomycetes is of great importance to extend our understanding of their ecology, taxonomy and bioactivity. 相似文献
1000.
To investigate the interaction of the surface of biomembranes with solvents systematically, we have studied the structure and phase behavior of multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) in dimethylformamide (DMF)-water mixture by X-ray diffraction and differential scanning calorimetry. The solubility of phosphorylcholine, which is the same molecular structure as the head-group of phosphatidylcholine (PC), decreased with an increase in DMF concentration. This result indicates that DMF is a poor solvent for the hydrophilic segments of the surface of the PC membrane, and interaction free energy of the hydrophilic segments of the membrane surface with solvents increases with an increase in DMF concentration. X-ray diffraction data indicated that DPPC-MLVs were in the bilayer gel phase from 0 to 80% (v/v) DMF, and that the spacing (lamellar repeat period) and intermembrane distance of DPPC-MLV decreased with an increase in DMF concentration. Main transition temperature and pre-transition temperature of DPPC-MLV increased with an increase in DMF concentration, and above 50% (v/v) DMF there was no pre-transition. In the interaction of POPC-MLV with DMF, X-ray diffraction data indicated that POPC-MLVs were in L(alpha) phase (liquid-crystalline phase) from 0 to 80% (v/v) DMF, and that the spacing and intermembrane distance of POPC-MLV decreased with an increase in DMF concentration. These results are discussed by the change of the interaction free energy between the hydrophilic segments of the membrane surface and solvents. As DMF concentration increases, this interaction free energy may increase, resulting in the decrease of the intermembrane distance of PC-MLVs. 相似文献