全文获取类型
收费全文 | 392364篇 |
免费 | 49457篇 |
国内免费 | 271篇 |
出版年
2020年 | 4104篇 |
2019年 | 5847篇 |
2018年 | 7795篇 |
2017年 | 7567篇 |
2016年 | 9332篇 |
2015年 | 11926篇 |
2014年 | 12258篇 |
2013年 | 16643篇 |
2012年 | 16649篇 |
2011年 | 16236篇 |
2010年 | 12275篇 |
2009年 | 9679篇 |
2008年 | 13614篇 |
2007年 | 13273篇 |
2006年 | 12482篇 |
2005年 | 11916篇 |
2004年 | 11509篇 |
2003年 | 10923篇 |
2002年 | 10403篇 |
2001年 | 13647篇 |
2000年 | 13548篇 |
1999年 | 10871篇 |
1998年 | 4045篇 |
1997年 | 4133篇 |
1996年 | 3948篇 |
1995年 | 3582篇 |
1994年 | 3575篇 |
1993年 | 3466篇 |
1992年 | 8836篇 |
1991年 | 8788篇 |
1990年 | 8331篇 |
1989年 | 8213篇 |
1988年 | 7588篇 |
1987年 | 7232篇 |
1986年 | 6571篇 |
1985年 | 6845篇 |
1984年 | 5704篇 |
1983年 | 4807篇 |
1982年 | 3741篇 |
1981年 | 3503篇 |
1979年 | 5436篇 |
1978年 | 4193篇 |
1977年 | 4064篇 |
1976年 | 3757篇 |
1975年 | 4158篇 |
1974年 | 4573篇 |
1973年 | 4494篇 |
1972年 | 3954篇 |
1971年 | 3723篇 |
1970年 | 3344篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
31.
32.
Ca2+ channel antagonist actions in bladder smooth muscle: comparative pharmacologic and [3H]nitrendipine binding studies 总被引:2,自引:0,他引:2
F B Yousif G T Bolger A Ruzycky D J Triggle 《Canadian journal of physiology and pharmacology》1985,63(5):453-462
The actions of a series of 15 Ca2+ channel antagonists including D-600, nifedipine, and diltiazem were examined against K+ depolarization and muscarinic receptor induced responses in guinea pig bladder smooth muscle. Responses of bladder are very dependent upon extracellular Ca2+ and sensitive to the Ca2+ channel antagonists, the tonic component more than the phasic component of response. Regardless of stimulant, K+ or methylfurmethide (MF), or component of response, the same rank order of antagonist activities is expressed, suggestive of a single structure-activity relationship and the existence of a single category of binding site which may, however, exist in several affinity states. High affinity binding of [3H]nitrendipine (KD = 1.1 X 10(-10) M) occurs in bladder membranes, and similar high affinity binding was found in microsomal preparations from other smooth muscles including guinea pig and rat lung, rat vas deferens, uterus, and stomach. [3H]nitrendipine binding in the bladder was sensitive to displacement by other 1,4-dihydropyridines, paralleling their pharmacologic activities and showing excellent agreement with binding data previously obtained for guinea pig ileal smooth muscle. Comparison of pharmacologic data for inhibition of K+- and MF-induced responses by a common series of Ca2+ channel antagonists in bladder and ileum revealed excellent correlations. Neither pharmacologic nor binding studies suggest significant differences in Ca2+ channel antagonist properties in smooth muscle from bladder and intestine. 相似文献
33.
34.
35.
Auxotrophic mutants of Candida albicans FC18 were induced by a combination of treatments with nitrous acid and UV irradiation. Arginine (Arg-), histidine (His-) and methionine/cysteine (MetA-) auxotrophs were recovered by this means. The Arg- auxotrophs lacked active argininosuccinate lyase (EC 4.3.2.1), the enzyme catalysing the final step in arginine biosynthesis. Thus the locus may be designated arg-4. The mutant strains bearing this mutation did not form germ tubes unless the germination medium contained arginine. 相似文献
36.
37.
Nonintegrative transformation in the filamentous fungus Podospora anserina: stabilization of a linear vector by the chromosomal ends of Tetrahymena thermophila. 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The effect of the chromosomal ends of Tetrahymena thermophila on the stability of linear transforming molecules in the filamentous fungus Podospora anserina was tested. A derivative of an integrative vector for this fungus has been constructed, so that after linearization, the ends of the plasmid are the telomeric sequences of T. thermophila. After transformation, this linear molecule was maintained as an extrachromosomal plasmid with no integrated copies in about 50% of the transformants. Under selective conditions, there was approximately one linear molecule per 5 to 10 nuclei, and these extrachromosomal molecules were rapidly lost under nonselective conditions. The circular plasmid carrying an inverted repeat of T. thermophila telomeres could be linearized and processed in vivo. 相似文献
38.
V K Khugaeva E D Klimenko P N Aleksandrov G F Leskova M I Reutov 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(7):15-19
Experiments were made on rabbit fed an atherogenic diet (0.5 g/kg cholesterol) singly for 15 and 24 h and repeatedly for 3, 9 and 30 days. At early stages of lipid metabolism distress the interrelationship was established between blood rheological disorders and microcirculatory abnormalities. The dependence of the initial reaction of some rheological characteristics on their initial level was marked. 相似文献
39.
40.
Jessica L. Hite Alaina C. Pfenning‐Butterworth Rachel E. Vetter Clayton E. Cressler 《Ecology and evolution》2020,10(13):6239-6245
- Food ingestion is one of the most basic features of all organisms. However, obtaining precise—and high‐throughput—estimates of feeding rates remains challenging, particularly for small, aquatic herbivores such as zooplankton, snails, and tadpoles. These animals typically consume low volumes of food that are time‐consuming to accurately measure.
- We extend a standard high‐throughput fluorometry technique, which uses a microplate reader and 96‐well plates, as a practical tool for studies in ecology, evolution, and disease biology. We outline technical and methodological details to optimize quantification of individual feeding rates, improve accuracy, and minimize sampling error.
- This high‐throughput assay offers several advantages over previous methods, including i) substantially reduced time allotments per sample to facilitate larger, more efficient experiments; ii) technical replicates; and iii) conversion of in vivo measurements to units (mL‐1 hr‐1 ind‐1) which enables broad‐scale comparisons across an array of taxa and studies.
- To evaluate the accuracy and feasibility of our approach, we use the zooplankton, Daphnia dentifera, as a case study. Our results indicate that this procedure accurately quantifies feeding rates and highlights differences among seven genotypes.
- The method detailed here has broad applicability to a diverse array of aquatic taxa, their resources, environmental contaminants (e.g., plastics), and infectious agents. We discuss simple extensions to quantify epidemiologically relevant traits, such as pathogen exposure and transmission rates, for infectious agents with oral or trophic transmission.