全文获取类型
收费全文 | 477575篇 |
免费 | 160946篇 |
国内免费 | 29804篇 |
专业分类
668325篇 |
出版年
2018年 | 5785篇 |
2016年 | 6664篇 |
2015年 | 8246篇 |
2014年 | 9406篇 |
2013年 | 12861篇 |
2012年 | 14041篇 |
2011年 | 14946篇 |
2010年 | 12432篇 |
2009年 | 16538篇 |
2008年 | 14310篇 |
2007年 | 14818篇 |
2006年 | 13091篇 |
2005年 | 12618篇 |
2004年 | 12705篇 |
2003年 | 12050篇 |
2002年 | 12567篇 |
2001年 | 21173篇 |
2000年 | 19133篇 |
1999年 | 19959篇 |
1998年 | 12761篇 |
1997年 | 12800篇 |
1996年 | 11918篇 |
1995年 | 12009篇 |
1994年 | 11402篇 |
1993年 | 11100篇 |
1992年 | 18681篇 |
1991年 | 18415篇 |
1990年 | 19128篇 |
1989年 | 18216篇 |
1988年 | 16876篇 |
1987年 | 15505篇 |
1986年 | 14487篇 |
1985年 | 14458篇 |
1984年 | 11717篇 |
1983年 | 9879篇 |
1982年 | 8531篇 |
1981年 | 7640篇 |
1980年 | 7292篇 |
1979年 | 10749篇 |
1978年 | 8750篇 |
1977年 | 8315篇 |
1976年 | 7951篇 |
1975年 | 8050篇 |
1974年 | 8871篇 |
1973年 | 8729篇 |
1972年 | 8500篇 |
1971年 | 7753篇 |
1970年 | 6796篇 |
1969年 | 6806篇 |
1968年 | 6165篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
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
93.
94.
95.
96.
Donald E. Rivett Dean Hewish Alan Kirkpatrick Jerome Werkmeister 《Journal of Protein Chemistry》1999,18(3):291-295
Nine fatty acid–peptide hybrid molecules were constructed using the general formula CH3(CH2)
n
CO-Phe Asp Cys-amide and tested for their ability to inhibit cell lysis induced by the membrane-active peptide melittin. All of these molecules, where n = 4–14, inhibited the action of melittin to some extent, but the longer carbon chains were most effective. Several potential inhibitors were also constructed with conservative substitutions in the peptide portion of the molecule. All were effective to varying degrees. We concluded that in the hexapeptide inhibitor published by Blondelle et al. (1993), the role of the first three residues is only to provide hydrophobic interaction with the melittin and has no particular amino acid sequence specificity. Some of these inhibitors were found to inhibit the lytic activity of a melittin analogue which had only superficial sequence similarity to melittin and also a truncated form of melittin, indicating the generality of the action of the inhibitors.Deceased 5/4/98 相似文献
97.
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
98.
99.
100.