全文获取类型
收费全文 | 346845篇 |
免费 | 39778篇 |
国内免费 | 155篇 |
专业分类
386778篇 |
出版年
2018年 | 3310篇 |
2017年 | 3116篇 |
2016年 | 4625篇 |
2015年 | 6518篇 |
2014年 | 7521篇 |
2013年 | 10416篇 |
2012年 | 11900篇 |
2011年 | 12109篇 |
2010年 | 8039篇 |
2009年 | 7092篇 |
2008年 | 10348篇 |
2007年 | 10742篇 |
2006年 | 10136篇 |
2005年 | 9573篇 |
2004年 | 9674篇 |
2003年 | 9257篇 |
2002年 | 9104篇 |
2001年 | 14547篇 |
2000年 | 14504篇 |
1999年 | 11718篇 |
1998年 | 4302篇 |
1997年 | 4331篇 |
1996年 | 4109篇 |
1995年 | 3952篇 |
1994年 | 3937篇 |
1993年 | 3820篇 |
1992年 | 9898篇 |
1991年 | 9519篇 |
1990年 | 9306篇 |
1989年 | 9024篇 |
1988年 | 8421篇 |
1987年 | 8049篇 |
1986年 | 7286篇 |
1985年 | 7404篇 |
1984年 | 6130篇 |
1983年 | 5383篇 |
1982年 | 4276篇 |
1981年 | 3796篇 |
1980年 | 3588篇 |
1979年 | 6151篇 |
1978年 | 4588篇 |
1977年 | 4315篇 |
1976年 | 4011篇 |
1975年 | 4337篇 |
1974年 | 4695篇 |
1973年 | 4752篇 |
1972年 | 4376篇 |
1971年 | 4088篇 |
1970年 | 3459篇 |
1969年 | 3351篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
982.
Effect of dietary cis and trans fatty acids on serum lipoprotein[a] levels in humans. 总被引:4,自引:0,他引:4
Serum lipoprotein[a] (Lp[a]) is a strong risk factor for coronary heart disease. We therefore examined the effect of dietary fatty acid composition on serum Lp[a] levels in three strictly controlled experiments with healthy normocholesterolemic men and women. In Expt. I, 58 subjects consumed a control diet high in saturated fatty acids for 17 days. For the next 36 days, 6.5% of total energy intake from saturated fatty acids was replaced by monounsaturates plus polyunsaturates (monounsaturated fatty acid diet; n = 29) or by polyunsaturates alone (polyunsaturated fatty acid diet; n = 29). Both diets caused a slight, nonsignificant, increase in median Lp[a] levels, with no difference between diets. In Expt. II, 10% of energy from the cholesterol-raising saturated fatty acids (lauric, myristic, and palmitic acid) was replaced by oleic acid or by trans-monounsaturated fatty acids. Each of the 59 participants received each diet for 3 weeks in random order. The median level of Lp[a] was 26 mg/l on the saturated fatty acid diet; it increased to 32 mg/l (P less than 0.020) on the oleic acid diet and to 45 mg/l (P less than 0.001) on the trans-fatty acid diet. The difference in Lp[a] between the trans-fatty acid and the oleic acid diets was also highly significant (P less than 0.001). Expt. III involved 56 subjects; all received 8% of energy from stearic acid, from linoleic acid, or from trans-monounsaturates, for 3 weeks each. All other nutrients were equal.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
983.
In this paper, we present a model for the development of connections between muscle afferents and motoneurones in the human spinal cord. The model consists of a limb with six muscles, one motoneurone pool, one pooled (Ia-like) afferent for each muscle and a central programme generator. The weights of the connections between the afferents and the motoneurone pools are adapted during centrally induced movements of the limb. The connections between the afferents and the motoneurone pools adapt in a hebbian way, using only local information present at the synapses. This neural network is tested in two examples of a limb with two degrees of freedom and six muscles. Despite the simplifications, the model predicts the pattern of autogenic and heterogenic monosynaptic reflexes quite realistically. 相似文献
984.
Subgenomic mRNA in OK10 Defective Leukemia Virus-Transformed Cells 总被引:16,自引:6,他引:10
S. Saule A. Sergeant G. Torpier M. B. Raes S. Pfeifer D. Stehelin 《Journal of virology》1982,42(1):71-82
985.
Thrombin is released as a soluble enzyme from the surface of platelets and tissue-factor-bearing cells to trigger fibrin polymerization during thrombosis under flow conditions. Although isotropic fibrin polymerization under static conditions involves protofibril extension and lateral aggregation leading to a gel, factors regulating fiber growth are poorly quantified under hemodynamic flow due to the difficulty of setting thrombin fluxes. A membrane microfluidic device allowed combined control of both thrombin wall flux (10−13 to 10−11 nmol/μm2 s) and the wall shear rate (10-100 s−1) of a flowing fibrinogen solution. At a thrombin flux of 10−12 nmol/μm2 s, both fibrin deposition and fiber thickness decreased as the wall shear rate increased from 10 to 100 s−1. Direct measurement and transport-reaction simulations at 12 different thrombin flux-wall shear rate conditions demonstrated that two dimensionless numbers, the Peclet number (Pe) and the Damkohler number (Da), defined a state diagram to predict fibrin morphology. For Da < 10, we only observed thin films at all Pe. For 10 < Da < 900, we observed either mat fibers or gels, depending on the Pe. For Da > 900 and Pe < 100, we observed three-dimensional gels. These results indicate that increases in wall shear rate quench first lateral aggregation and then protofibril extension. 相似文献
986.
Two cases of trisomy 16 confined to placental tissue associated with an unfavourable outcome of the pregnancy are reported. In the first case, after a diagnosis of an apparent non-mosaic trisomy 16 at chorionic villi sample (CVS), an intrauterine fetal death occurred at the 22nd week. In the second case a mosaic with trisomy 16 was found in chorionic villi and the fetus was still-born at 38 weeks. From a comparison of their cases with those of the literature, the authors conclude that a trisomy 16 confined to placental tissue has a negative effect on fetal growth and pregnancy outcome. 相似文献
987.
988.
989.
Andrew W. Saxe Ji-Won Yoon Phillip Gorden Murray F. Brennan 《In vitro cellular & developmental biology. Plant》1982,18(10):884-890
Summary Dispersed cells from both fresh and cryopreserved human insulinoma have been maintained in cell culture. Initial yield of
viable cells was 50% for fresh and 25% for cryopreserved tissue. Viability of cells in culture was documented by increasing
numbers of cells (doubling time approximately 5 d initially and 2 d at the sixth subculture for both fresh and cryopreserved
tissue) and continued release of insulin over time (approximately 100 ng/ml per 105 cells at 10 d and 175 ng/ml per 105 cells at 30 d of culture for both fresh and cryopreserved tissue). Evidence that cells growing in culture were beta cells
was provided by: (a) recovery of intracellular and extracellular immunoreactive insulin (IRI), (b) electron microscopic morphology,
and (c) immunohistochemical staining. Cells from fresh insulinoma incubated with increasing concentrations of extracellular
glucose released increasing amounts of IRI up to approximately 15 mM glucose, which paralleled changes in plasma insulin obtained during a preoperative glucose tolerance test.
Under an Intergovernmental Personnel Act Exchange from the Department of Surgery, University of California, Davis, Sacramento
Medical Center. 相似文献
990.