全文获取类型
收费全文 | 3471篇 |
免费 | 208篇 |
国内免费 | 4篇 |
专业分类
3683篇 |
出版年
2022年 | 29篇 |
2021年 | 45篇 |
2020年 | 40篇 |
2019年 | 35篇 |
2018年 | 63篇 |
2017年 | 47篇 |
2016年 | 66篇 |
2015年 | 125篇 |
2014年 | 122篇 |
2013年 | 166篇 |
2012年 | 213篇 |
2011年 | 190篇 |
2010年 | 151篇 |
2009年 | 127篇 |
2008年 | 173篇 |
2007年 | 188篇 |
2006年 | 181篇 |
2005年 | 152篇 |
2004年 | 164篇 |
2003年 | 148篇 |
2002年 | 125篇 |
2001年 | 40篇 |
2000年 | 44篇 |
1999年 | 45篇 |
1998年 | 41篇 |
1997年 | 22篇 |
1996年 | 29篇 |
1995年 | 46篇 |
1994年 | 27篇 |
1993年 | 31篇 |
1992年 | 18篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 13篇 |
1983年 | 20篇 |
1982年 | 29篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 20篇 |
1976年 | 16篇 |
1971年 | 14篇 |
1962年 | 13篇 |
1912年 | 19篇 |
排序方式: 共有3683条查询结果,搜索用时 15 毫秒
61.
Methanosarcina barkeri (strain MS) grew and converted acetate to CO2 and methane after an adaption period of 20 days. Growth and metabolism were rapid with gas production being comparable to that of cells grown on H2 and CO2. After an intermediary growth cycle under a H2 and CO2 atmosphere acetateadapted cells were capable of growth on acetate with formation of methane and CO2. When acetate-adapted Methanosarcina barkeri was co-cultered with Acetobacterium woodii on fructose or glucose as substrate, a complete conversion of the carbohydrate to gases (CO2 and CH4) was observed.Abbreviation CMC
carboxymethyl cellulose 相似文献
62.
63.
Treatment of d-glucono-1,5-lactone (3) with excess of acetic anhydride in anhydrous pyridine at room temperature afforded the tetra-acetate and 2,4,6-tri-O-acetyl-3-deoxy-d-erythro-hex-2-enono-1,5-lactone (1). On prolonged reaction or at 80°, 3-acetoxy-6-acetoxymethylpyran-2-one (5) was the unexpected main product. The mechanistic implications of the conversion of 1 → 5 are discussed. 相似文献
64.
Ultrathin sectioning of submerged mycelium of Claviceps purpurea Tul. producing clavine alkaloids revealed yeast-like budding resulting in asexual sporesblastospores. These deciduous spores were born by extended hyphal cells and retained the same ultrastructure of cell organelles. Both the extended hyphae and the blastospores resembled the cells of ergot sclerotial tissue. A surface culture of C. purpurea Tul. producing no alkaloids was used as a reference. 相似文献
65.
An E. coli vector system was constructed which allows the expression of fusion genes via a l-rhamnose-inducible promotor. The corresponding fusion proteins consist of the maltose-binding protein and a His-tag sequence
for affinity purification, the Saccharomyces cerevisiae Smt3 protein for protein processing by proteolytic cleavage and the protein of interest. The Smt3 gene was codon-optimized
for expression in E. coli. In a second rhamnose-inducible vector, the S. cerevisiae Ulp1 protease gene for processing Smt3 fusion proteins was fused in the same way to maltose-binding protein and His-tag sequence
but without the Smt3 gene. The enhanced green fluorescent protein (eGFP) was used as reporter and protein of interest. Both
fusion proteins (MalE-6xHis-Smt3-eGFP and MalE-6xHis-Ulp1) were efficiently produced in E. coli and separately purified by amylose resin. After proteolytic cleavage the products were applied to a Ni-NTA column to remove
protease and tags. Pure eGFP protein was obtained in the flow-through of the column in a yield of around 35% of the crude
cell extract. 相似文献
66.
Arrhenotokously reproducing Hymenoptera and Acarina include many important natural enemies. This reproductive system offers
the opportunity of selection on hemizygous (♂ ♂), with the attendant advantages of an unmasked genotype fully exposed to selection,
in creased frequency of genotypes expressing rare genes, and enhanced discrimination of characters, in all-♂ populations produced
by virgin (♀ ♀). Increased selection intensity and reduced genetic drift may offer additional advantages. The method is limited
to characters displayed by (♂ ♂), and may require labor-intensive techniques and species-specific research. The method has
been shown to be practicable withAphytis holoxanthus DeBach (Hymenoptera: Aphelinidae), an important parasite of the Florida red scale,Chrysomphalus aonidum (L.) (Homoptera: Diaspididae).
相似文献
67.
Franzen C Fischer S Schroeder J Schölmerich J Schneuwly S 《The Journal of eukaryotic microbiology》2005,52(2):141-152
A new species of microsporidia from Drosophila melanogaster was investigated by light and electron microscopy and by ribosomal RNA (rRNA) sequencing. This microsporidium and the previously described Nosema kingi and Nosema acridophagus have been transferred to the new genus Tubulinosema gen. nov. with the following characters: nuclei are in diplokaryotic arrangement during the life cycle. All stages are in direct contact with the host cell cytoplasm, slightly anisofilar polar tube with the last coils being smaller in diameter arranged in one or two rows on both sides of the diplokaryon and small tubuli on the surface of late meronts. Spores are oval or slightly pyriform. Thick endospore wall, thinner over anchoring disc. This new genus and the genus Brachiola have been placed in a new family Tubulinosematidae fam. nov. Phylogenetic analysis of small subunit rRNA sequences by different methods placed Tubulinosema spp. in one clade with the genus Brachiola forming its sister clade, which is distant from the clade containing the true Nosema spp. including Nosema bombycis. 相似文献
68.
The occipital cortex (OC) of early-blind humans is activated during various nonvisual perceptual and cognitive tasks, but little is known about its modular organization. Using functional MRI we tested whether processing of auditory versus tactile and spatial versus nonspatial information was dissociated in the OC of the early blind. No modality-specific OC activation was observed. However, the right middle occipital gyrus (MOG) showed a preference for spatial over nonspatial processing of both auditory and tactile stimuli. Furthermore, MOG activity was correlated with accuracy of individual sound localization performance. In sighted controls, most of extrastriate OC, including the MOG, was deactivated during auditory and tactile conditions, but the right MOG was more activated during spatial than nonspatial visual tasks. Thus, although the sensory modalities driving the neurons in the reorganized OC of blind individuals are altered, the functional specialization of extrastriate cortex is retained regardless of visual experience. 相似文献
69.
Free radical formation in the cochlea plays a key role in the development of noise-induced hearing loss (NIHL). The amount, distribution, and time course of free radical formation have been defined, including a clinically significant formation of both reactive oxygen species and reactive nitrogen species 7-10 days after noise exposure. Reduction in cochlear blood flow as a result of free radical formation has also been described. Here we report that the antioxidant agents vitamins A, C, and E act in synergy with magnesium to effectively prevent noise-induced trauma. Neither the antioxidant agents nor the magnesium reliably reduced NIHL or sensory cell death with the doses we used when these agents were delivered alone. In combination, however, they were highly effective in reducing both hearing loss and cell death even with treatment initiated just 1 h before noise exposure. This study supports roles for both free radical formation and noise-induced vasoconstriction in the onset and progression of NIHL. Identification of this safe and effective antioxidant intervention that attenuates NIHL provides a compelling rationale for human trials in which free radical scavengers are used to eliminate this single major cause of acquired hearing loss. 相似文献
70.
Josef Trögl Ivana Jirková Petra Zemánková Věra Pilařová Petra Dáňová Jana Pavlorková Pavel Kuráň Jan Popelka Lucie Křiklavová 《Folia microbiologica》2013,58(2):135-140
The content of phospholipid fatty acids (PLFA) was determined in samples of polyvinyl alcohol lenses (Lentikats Biocatalyst, LB) with encapsulated Paracoccus denitrificans withdrawn during long-term denitrification experiments. The total PLFA content correlated highly with specific denitrification activities of LB as well as biomass estimation based on image analyses of microscopic photos. The results confirmed the applicability of PLFA determination for estimation of the amount of living encapsulated microbial biomass during biotechnological applications. 相似文献