全文获取类型
收费全文 | 420163篇 |
免费 | 43679篇 |
国内免费 | 196篇 |
专业分类
464038篇 |
出版年
2016年 | 4519篇 |
2015年 | 5956篇 |
2014年 | 7058篇 |
2013年 | 10623篇 |
2012年 | 11493篇 |
2011年 | 11973篇 |
2010年 | 8151篇 |
2009年 | 7482篇 |
2008年 | 10691篇 |
2007年 | 11348篇 |
2006年 | 10680篇 |
2005年 | 10160篇 |
2004年 | 10258篇 |
2003年 | 10022篇 |
2002年 | 9825篇 |
2001年 | 17352篇 |
2000年 | 17394篇 |
1999年 | 14055篇 |
1998年 | 4979篇 |
1997年 | 5288篇 |
1996年 | 5015篇 |
1995年 | 4730篇 |
1994年 | 4635篇 |
1993年 | 4634篇 |
1992年 | 12269篇 |
1991年 | 12072篇 |
1990年 | 12087篇 |
1989年 | 11860篇 |
1988年 | 11165篇 |
1987年 | 10502篇 |
1986年 | 9822篇 |
1985年 | 10242篇 |
1984年 | 8441篇 |
1983年 | 7280篇 |
1982年 | 5615篇 |
1981年 | 5021篇 |
1980年 | 4694篇 |
1979年 | 8082篇 |
1978年 | 6303篇 |
1977年 | 5944篇 |
1976年 | 5675篇 |
1975年 | 6132篇 |
1974年 | 6701篇 |
1973年 | 6569篇 |
1972年 | 6123篇 |
1971年 | 5537篇 |
1970年 | 4767篇 |
1969年 | 4783篇 |
1968年 | 4454篇 |
1967年 | 3810篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
G S Aulakh E B Stephens D L Rose J G Tully M F Barile 《Journal of bacteriology》1983,153(3):1338-1341
3H-labeled Acholeplasma DNA probes were generated in vitro by the nick-translation method and used to determine the nucleotide sequence homology among the type strains of the eight currently recognized species of Acholeplasma. Very little nucleotide sequence homology (less than or equal to 18%) was found among the eight species, with heteroduplexes showing at least 12% or more mismatching as determined by thermal elution midpoints. The small amount of nucleotide sequence homology among the eight species indicates that these species are quite distinct and are not closely related to each other genomically. 相似文献
72.
Monosomy 21: a new case confirmed by in situ hybridization 总被引:4,自引:0,他引:4
M. C. Pellissier N. Philip M. A. Voelckel-Baeteman M. G. Mattei J. F. Mattei 《Human genetics》1987,75(1):95-96
Summary A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation. 相似文献
73.
A series of measurements of blood pressure in normotensive and hypertensive subjects showed that measurements made with a sphygmomanometer with the arm dependent by the side were consistently higher than those made with the arm horizontal at heart level. The mean difference in a group of 90 hypertensive outpatients was 11/12 mm Hg. Failure to appreciate the importance of arm position may lead to erroneous measurements of blood pressure. This has important implications for clinical practice and research. 相似文献
74.
75.
Genes for the biosynthesis of spinosyns: applications for yield improvement in Saccharopolyspora spinosa 总被引:2,自引:0,他引:2
K Madduri C Waldron P Matsushima M C Broughton K Crawford D J Merlo R H Baltz 《Journal of industrial microbiology & biotechnology》2001,27(6):399-402
Spinosyns A and D are the active ingredients in an insect control agent produced by fermentation of Saccharopolyspora spinosa. Spinosyns are macrolides with a 21-carbon, tetracyclic lactone backbone to which the deoxysugars forosamine and tri-O-methylrhamnose are attached. The spinosyn biosynthesis genes, except for the rhamnose genes, are located in a cluster that
spans 74 kb of the S. spinosa genome. DNA sequence analysis, targeted gene disruptions and bioconversion studies identified five large genes encoding type
I polyketide synthase subunits, and 14 genes involved in sugar biosynthesis, sugar attachment to the polyketide or cross-bridging
of the polyketide. Four rhamnose biosynthetic genes, two of which are also necessary for forosamine biosynthesis, are located
outside the spinosyn gene cluster. Duplication of the spinosyn genes linked to the polyketide synthase genes stimulated the
final step in the biosynthesis — the conversion of the forosamine-less pseudoaglycones to endproducts. Duplication of genes
involved in the early steps of deoxysugar biosynthesis increased spinosyn yield significantly. Journal of Industrial Microbiology & Biotechnology (2001) 27, 399–402.
Received 31 May 2001/ Accepted in revised form 09 July 2001 相似文献
76.
77.
78.
Mechanisms of changes in human hemodynamics under the conditions of microgravity and prognosis of postflight orthostatic stability 总被引:1,自引:0,他引:1
The mechanisms of hemodynamic responses to orthostatic stresses and orthostatic stability (OS) of cosmonauts were studied before and after short-and long-term spaceflights (SFs) using orthostatic tests, as well as before, during, and after SFs using ultrasonic methods in tests with exposure to lower body negative pressure (LBNP). The capacitance and distensibility of the veins of the lower extremities were studied using occlusive air plethysmography before, during, and after SFs of different durations. A stay in microgravity has been proved to result in detraining of, mainly, the vascular mechanisms of compensating orthostatic perturbations. It has been established that the decrease in OS under the influence of microgravity is determined by a reduction of the vasoconstrictive ability of large blood vessels of the lower extremities; an increase in venous distensibility and capacitance of the legs; and an impairment of blood flow regulation, which leads to a cerebral blood flow deficit in orthostatic stresses, and of the initial individual OS before the flight. The results of preflight studies of hemodynamics by ultrasonic methods at LBNP and the data of orthostatic tests before SFs make it possible to predict the degree of decrease of OS after an SF proceeding in the normal mode. At the same time, the data of ultrasonic blood flow examination provide more a accurate estimation of OS and make it possible to assess the physiological reserves of hemodynamic regulation and to reveal the loss of regulation capacity even in cases where integrated indices (heart rate and blood pressure) are within the normal ranges. 相似文献
79.
80.