全文获取类型
收费全文 | 85865篇 |
免费 | 7583篇 |
国内免费 | 46篇 |
专业分类
93494篇 |
出版年
2023年 | 281篇 |
2022年 | 707篇 |
2021年 | 1548篇 |
2020年 | 880篇 |
2019年 | 1108篇 |
2018年 | 1439篇 |
2017年 | 1241篇 |
2016年 | 2136篇 |
2015年 | 3630篇 |
2014年 | 4047篇 |
2013年 | 4811篇 |
2012年 | 6536篇 |
2011年 | 6481篇 |
2010年 | 4170篇 |
2009年 | 3798篇 |
2008年 | 5429篇 |
2007年 | 5432篇 |
2006年 | 5233篇 |
2005年 | 5031篇 |
2004年 | 4892篇 |
2003年 | 4667篇 |
2002年 | 4402篇 |
2001年 | 857篇 |
2000年 | 623篇 |
1999年 | 960篇 |
1998年 | 1230篇 |
1997年 | 821篇 |
1996年 | 742篇 |
1995年 | 653篇 |
1994年 | 616篇 |
1993年 | 667篇 |
1992年 | 553篇 |
1991年 | 520篇 |
1990年 | 461篇 |
1989年 | 398篇 |
1988年 | 421篇 |
1987年 | 342篇 |
1986年 | 317篇 |
1985年 | 399篇 |
1984年 | 518篇 |
1983年 | 401篇 |
1982年 | 501篇 |
1981年 | 486篇 |
1980年 | 414篇 |
1979年 | 295篇 |
1978年 | 323篇 |
1977年 | 281篇 |
1976年 | 263篇 |
1975年 | 204篇 |
1974年 | 241篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
152.
153.
154.
155.
156.
Michael F. Myers 《CMAJ》1965,92(17):926-927
Sweat chlorides of 10 sets of parents of children with cystic fibrosis and 11 controls were studied in an attempt to develop a test for the diagnosis of cystic fibrosis heterozygotes by subjecting both the parents and controls to a low sodium diet and comparing sweat chloride values as the diet progressed. It was hoped that the sweat chloride levels of the parents, the heterozygotes, would remain stationary throughout the diet, since their children, the homozygotes, reveal this finding under similar conditions of salt deprivation. The sweat chloride levels of the controls, because of effects of aldosterone, were expected to decrease steadily from the commencement of the diet to its termination.A decrease in sweat chloride values of similar magnitude was found in both parents and controls as the diet continued. It is concluded that the study of sweat electrolyte levels in salt-deprived subjects is of no value in the diagnosis of cystic fibrosis heterozygotes. 相似文献
157.
The antioxidant capacity of 5-hydroxy-tryptophan. 5-hydroxy-indole. and DOPA (3,4-dihydroxy-phenyI-alanine) was tested in the Fe-induced lipid peroxidation of liver microsomes of normal- and vitamin E-deficient rats, using ascorbate as a reductant. Lipid peroxidation was monitored as low-level chemilu-minescence, indicative of generation of electronically-excited states arising from the recombination of secondary lipid peroxyl radicals. 相似文献
158.
Summary The molecular evolution of cytochrome c from angiosperms is compared to that from vertebrates. On the basis of a cladistic
analysis from 26 plant species, compared to that from 27 vertebrate species, we find that although the vertebrate sequences
yield reasonably well-defined minimal trees that are congruent with the biological tree, the plant sequences yield multiple
minimal trees that are not only highly incongruent with each other, but none of which is congruent with any reasonably biological
tree. That is, the plant sequence set is much more homoplastic than that of the animal. However, as judged by the relative
rate test, the extent of divergence, and degree of functional constraint, cytochrome c evolution in plants does not appear
to differ from that of vertebrates. 相似文献
159.
Release of recombinant microbes into the environment necessitates an evaluation of their ability to transfer genetic material. The present report evaluates a method to detect conjugal DNA plasmid transfer in soil slurries under various environmental conditions. DonorPseudomonas cepacia containing pR388::Tn1721 andP. cepacia recipient cultures were coincubated in soil slurries containing autoclaved or natural soil and treated with one or more of 14 experimental conditions. Conjugal mating frequency (transconjugants per initial donor) ranged from 4.8×10–1 to 1.9×10–7. Highest numbers of transconjugants, 1.5×107 colony forming units/ml soil slurry, were observed following incubation at 35°C with an enriched nutrient supplement added to the soil. Low numbers of transconjugants, 103 colony forming units/ml soil slurry, were observed when mating pairs were subjected to low nutrient or pH stress even though initial donor and recipient populations were maintained at high levels. This test system provides a simple way to estimate effects of changing environmental factors on plasmid transfer rates and on the survival of recombinant microorganisms. By use of soil collected from sites proposed to receive genetically engineered microorganisms, preliminary risk assessments can be obtained regarding the potential for gene transfer and microorganism survival with this soil slurry test system. 相似文献
160.
Comparability of two tests of olfactory functioning 总被引:2,自引:1,他引:1
In the first of two comparisons, 50 patients who came to theConnecticut Chemosensory Clinical Research Center (CCCRC) withvarious chemosensory complaints were evaluated by a dual threshold/odoridentification test administered in the CCCRC and by the self-administeredUniversity of Pennsylvania Smell Identification Test (UPSIT).Agreement between tests proved high, with a correlation coefficientof 0.92. The UPSIT correlated better with the odor identificationcomponent than with the threshold component of the CCCRC test.This disparity stemmed largely from limitations in the reliabilityof the threshold component. An increase in the stringency ofthe criterion for determination of threshold increased the reliabilityof this component and, in a second comparison with a total of58 patients and controls, the correlation between the UPSITand CCCRC test increased. With the more stringent criterion,the correlation equalled 0.96.
2Present address: International Flavors and Fragrances, Researchand Development, Union Beach, NJ 07735, USA 相似文献