全文获取类型
收费全文 | 137360篇 |
免费 | 22883篇 |
国内免费 | 10024篇 |
专业分类
170267篇 |
出版年
2024年 | 271篇 |
2023年 | 1537篇 |
2022年 | 3581篇 |
2021年 | 6200篇 |
2020年 | 5857篇 |
2019年 | 8250篇 |
2018年 | 8025篇 |
2017年 | 7113篇 |
2016年 | 8542篇 |
2015年 | 10667篇 |
2014年 | 11679篇 |
2013年 | 12509篇 |
2012年 | 12184篇 |
2011年 | 10904篇 |
2010年 | 8679篇 |
2009年 | 6928篇 |
2008年 | 6743篇 |
2007年 | 5676篇 |
2006年 | 4961篇 |
2005年 | 4009篇 |
2004年 | 3417篇 |
2003年 | 3117篇 |
2002年 | 2633篇 |
2001年 | 2226篇 |
2000年 | 1973篇 |
1999年 | 1916篇 |
1998年 | 1118篇 |
1997年 | 1093篇 |
1996年 | 999篇 |
1995年 | 876篇 |
1994年 | 840篇 |
1993年 | 662篇 |
1992年 | 872篇 |
1991年 | 658篇 |
1990年 | 502篇 |
1989年 | 472篇 |
1988年 | 376篇 |
1987年 | 361篇 |
1986年 | 290篇 |
1985年 | 305篇 |
1984年 | 165篇 |
1983年 | 171篇 |
1982年 | 102篇 |
1981年 | 86篇 |
1980年 | 61篇 |
1979年 | 78篇 |
1977年 | 59篇 |
1975年 | 56篇 |
1974年 | 52篇 |
1973年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
The neotype ofRepomucenus sagitta is described. Specimens conspecific with the neotype from India, the Gulf of Thailand, the South China Sea, the Yellow Sea
and Australia are described. Sexual characters, geographic variation, habitat and geographic distribution were noted.Repomucenus macdonaldi is a junior synonym ofR. sagitta as defined by the neotype. 相似文献
84.
A coronal plane model of a distributed elastic sole has been proposed and analyzed with respect to the effects of different medial-lateral elasticity distribution on pronation under quasi-static conditions. The distributed model consists of an array of linear vertical line springs. Under minimum energy assumption, the behavior of the top surface of the interface under resultant force and moment loading was shown to be equivalent to that of a rigid-body mechanism under the same loading. The model was then combined with a rigid-link model of the lower limb. Expressions that describe the relationship of the interface aggregate parameters with pronation and the center of pressure were obtained. These expressions were confirmed by an experiment in which the elastic distribution in the interface was systematically varied and the pronation angle and the center of pressure measured. The model has the potential of being a useful analytical tool in the design of elastic soles in running shoes. 相似文献
85.
Characteristics of high affinity uptake of L-glutamate are examined in order to evaluate the possible use of the uptake of [3H]L-glutamate, [3H]L-aspartate or any other suitable [3H]-labelled substrate as a marker for glutamatergic and aspartergic synapses in autoradiographic studies in the mammalian brain. Review of data on substrate specificity indicates the presence of at least two high affinity uptake systems specific for acidic amino acids in the central nervous tissue; one which takes up L-glutamate and L-aspartate and the other which is selective for L-glutamate only. Studies on ionic requirements, too, point to the existence of at least two distinct uptake systems with high affinity for L-glutamate. The Na(+)-dependent uptake system(s) handle(s) both L-glutamate and L-aspartate whereas the Na(+)-independent uptake system(s) show(s) selectivity for L-glutamate only. Available data do not favour the Na(+)-dependent binding of [3H]D-aspartate to thaw-mounted sections of frozen brain tissue as a suitable marker for glutamatergic/aspartergic synaptic nerve endings. However, there are reasons--such as the results of lesion studies and the existence of uptake sites which have a higher affinity for L-aspartate than for D-aspartate--to suggest that Na(+)-dependent binding of [3H]L-aspartate, rather than that of [3H]D-aspartate, should be further investigated as a possible marker for the glutamatergic/aspartergic synapses in the autoradiographic studies using sections of frozen brain. 相似文献
86.
87.
Z H Li T R Burke J B Bolen 《Biochemical and biophysical research communications》1991,180(2):1048-1056
Several styryl-based compounds were evaluated for their capacity to act as inhibitors of the non-receptor tyrosine protein kinase p56lck. Our results demonstrate that alpha-cyanocinnamamide compounds can inhibit both the in vitro tyrosine autophosphorylation of p56lck as well as p56lck phosphorylation of exogenous substrates. Compound 67B-83-A was found to inhibit p56lck protein kinase activity with a calculated IC50 of 7 to 10 microM. This compound did not significantly inhibit the tyrosine protein kinase activity of the epidermal growth factor receptor and was found to be a less effective tyrosine protein kinase inhibitor for other members of the src family of protein kinases. 相似文献
88.
玉米未成熟胚乳愈伤组织和器官的发生及其倍性变化的初步研究 总被引:2,自引:1,他引:1
本试验在附加和不附加外源激素的MS培养基上,均得到了玉米未成熟胚乳愈伤组织。愈伤组织在附加外源激素的MS培养基上达到器官分化,获得了发育正常的和许多畸形的胚乳植株。所得到的愈伤组织细胞和植株根尖细胞染色体数目和倍性是不稳定的,二者有相同的趋向,其中有整倍体的细胞(2n=10,20,30,40,50),也有各种非整倍体的细胞(2n=5—49)。 相似文献
89.
Y J Shyy Y S Li P E Kolattukudy 《Biochemical and biophysical research communications》1990,169(2):346-351
90.
For a long time, the evolutionary series of a idoraptids-dimorphograptids-monograptids has been generally recognized by graptolite researchers. In the past years, the akidograptids were found to appear in the Lower Silurian Parakidograptus acuminatus Zone, while the dimorphograptids in the P. acuminatus and Orthograpius vesiculosus Zones, but the monograptids appeared as late as in the O. vesiculosus zone; this evolutionary series can be easily accepted by other people. Chen Xu and Lin Yao-kun (1978) pu... 相似文献