全文获取类型
收费全文 | 16499篇 |
免费 | 2204篇 |
国内免费 | 8篇 |
出版年
2021年 | 183篇 |
2019年 | 170篇 |
2018年 | 201篇 |
2017年 | 179篇 |
2016年 | 300篇 |
2015年 | 480篇 |
2014年 | 548篇 |
2013年 | 656篇 |
2012年 | 770篇 |
2011年 | 834篇 |
2010年 | 541篇 |
2009年 | 516篇 |
2008年 | 672篇 |
2007年 | 654篇 |
2006年 | 565篇 |
2005年 | 597篇 |
2004年 | 614篇 |
2003年 | 562篇 |
2002年 | 526篇 |
2001年 | 512篇 |
2000年 | 557篇 |
1999年 | 462篇 |
1998年 | 199篇 |
1997年 | 206篇 |
1996年 | 183篇 |
1995年 | 195篇 |
1994年 | 198篇 |
1993年 | 180篇 |
1992年 | 390篇 |
1991年 | 388篇 |
1990年 | 381篇 |
1989年 | 339篇 |
1988年 | 324篇 |
1987年 | 298篇 |
1986年 | 250篇 |
1985年 | 272篇 |
1984年 | 229篇 |
1983年 | 214篇 |
1982年 | 169篇 |
1981年 | 167篇 |
1980年 | 154篇 |
1979年 | 235篇 |
1978年 | 199篇 |
1977年 | 187篇 |
1976年 | 179篇 |
1975年 | 177篇 |
1974年 | 170篇 |
1973年 | 188篇 |
1972年 | 177篇 |
1971年 | 165篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Fatty acids and monoglycerides were evaluated in brain heart infusion broth and in milk for antimicrobial activity against the Scott A strain of Listeria monocytogenes. C12:0, C18:3, and glyceryl monolaurate (monolaurin) had the strongest activity in brain heart infusion broth and were bactericidal at 10 to 20 micrograms/ml, whereas potassium (K)-conjugated linoleic acids and C18:2 were bactericidal at 50 to 200 micrograms/ml. C14:0, C16:0, C18:0, C18:1, glyceryl monomyristate, and glyceryl monopalmitate were not inhibitory at 200 micrograms/ml. The bactericidal activity in brain heart infusion broth was higher at pH 5 than at pH 6. In whole milk and skim milk, K-conjugated linoleic acid was bacteriostatic and prolonged the lag phase especially at 4 degrees C. Monolaurin inactivated L. monocytogenes in skim milk at 4 degrees C, but was less inhibitory at 23 degrees C. Monolaurin did not inhibit L. monocytogenes in whole milk because of the higher fat content. Other fatty acids tested were not effective in whole or skim milk. Our results suggest that K-conjugated linoleic acids or monolaurin could be used as an inhibitory agent against L. monocytogenes in dairy foods. 相似文献
12.
Kayla J. Vastenhout Ruthellen H. TornbergAmanda L. Johnson Michael W. AmolinsJared R. Mays 《Analytical biochemistry》2014
Isothiocyanates (ITCs) are one of several hydrolysis products of glucosinolates, plant secondary metabolites that are substrates for the thioglucohydrolase myrosinase. Recent pursuits toward the development of synthetic non-natural ITCs have consequently led to an exploration of generating these compounds from non-natural glucosinolate precursors. Evaluation of the myrosinase-dependent conversion of select non-natural glucosinolates to non-natural ITCs cannot be accomplished using established ultraviolet–visible (UV–Vis) spectroscopic methods. To overcome this limitation, an alternative high-performance liquid chromatography (HPLC)-based analytical approach was developed where initial reaction velocities were generated from nonlinear reaction progress curves. Validation of this HPLC method was accomplished through parallel evaluation of three glucosinolates with UV–Vis methodology. The results of this study demonstrate that kinetic data are consistent between both analytical methods and that the tested glucosinolates respond similarly to both Michaelis–Menten and specific activity analyses. Consequently, this work resulted in the complete kinetic characterization of three glucosinolates with Sinapis alba myrosinase, with results that were consistent with previous reports. 相似文献
13.
J R Lakowicz J Ku?ba W Wiczk I Gryczynski H Szmacinski M L Johnson 《Biophysical chemistry》1991,39(1):79-84
We report the first resolution of both the conformational distribution and end-to-end diffusion coefficient of a flexible molecule. This molecular information was recovered using only the donor intensity decay in a single solvent at a single viscosity, as observed by the technique of frequency-domain fluorometry. This technique can be extended to measurements of structural fluctuations of biological macromolecules. 相似文献
14.
15.
Russell R. Johnson Harwood J. Cranston Marta E. Chaverra William E. Dyer 《Plant molecular biology》1995,28(1):113-122
The molecular regulation of seed dormancy was investigated using differential display to visualize and isolate cDNAs representing differentially expressed genes during early imbibition of dormant and nondormant Avena fatua L. embryos. Of about 3000 cDNA bands examined, 5 cDNAs hybridized with mRNAs exhibiting dormancy-associated expression patterns during the first 48 h of imbibition, while many more nondormancy-associated cDNAs were observed. Dormancy-associated clone AFD1 hybridized with a 1.5 kb mRNA barely detectable in dry dormant and nondormant embryos that became more abundant in dormant embryos after 24 h of imbibition. Clone AFD2 hybridized with two mRNAs, a 1.3 kb message constitutively expressed in dormant and nondormant embryos and a 0.9 kb message present at higher levels in dormant embryos after 3 h of imbibition. Nondormancy-associated clones AFN1, AFN2 and AFN3 hybridized with 1.5 kb, 1.7 kb and 1.1 kb mRNAs, respectively, that were more abundant in nondormant embryos during imbibition. Expression patterns of some mRNAs in dormant embryos induced to germinate by GA3 treatment were different than water controls, but were not identical to those observed in nondormant embryos. DNA sequence analysis revealed 76% sequence identity between clone AFN3 and a Citrus sinensis glutathione peroxidase-like cDNA, while significant sequence similarities with known genes were not found for other clones. Southern hybridization analyses showed that all clones represent low (1 to 4) copy number genes. 相似文献
16.
Conflicting phylogenetic hypotheses for the parasitic platyhelminths tested by partial sequencing of 18S ribosomal RNA 总被引:1,自引:0,他引:1
P R Baverstock R Fielke A M Johnson R A Bray I Beveridge 《International journal for parasitology》1991,21(3):329-339
Partial sequencing of the 18S ribosomal RNA in nine parasitic and one free-living species of platyhelminth was used to test hypotheses on the phylogenetic relationships among the major groups. The eucestodes, amphilinideans, gyrocotylideans and monopisthocotylideans appeared as a monophyletic assemblage in a cladistic analysis of the data, with a very close association between the gyrocotylideans and monopisthocotylideans. The polyopisthocotylidean monogeneans were paraphyletic to the monopisthocotylideans. The digeneans appeared to be a sister group to the monogeneans and eucestodes, while the temnocephalidean was closely related to the free-living polyclad. 相似文献
17.
A crown-of-thorns starfish control program was conducted at Grub Reef (central Great Barrier Reef) in an area (0.64 km2) which encompassed 53 individual patch reefs. During a two week period, 15 divers injected 3175 starfish with copper sulphate. The program was considered unsuccessful. Although starfish abundance had declined significantly after the control efforts, biological surveys indicated that a relatively large number of starfish remained. The surveys also indicated a general decline in the number of starfish along the reef perimeter, outside the control area. The total cost of the control program was $35 per starfish. These results have important implications for the implementation of future control programs and highlight the need to undertake before and after biological surveys to assess the effectiveness of the control efforts. 相似文献
18.
19.
Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12