全文获取类型
收费全文 | 8165篇 |
免费 | 600篇 |
国内免费 | 142篇 |
出版年
2023年 | 72篇 |
2022年 | 194篇 |
2021年 | 362篇 |
2020年 | 191篇 |
2019年 | 233篇 |
2018年 | 284篇 |
2017年 | 233篇 |
2016年 | 277篇 |
2015年 | 436篇 |
2014年 | 466篇 |
2013年 | 614篇 |
2012年 | 637篇 |
2011年 | 575篇 |
2010年 | 321篇 |
2009年 | 291篇 |
2008年 | 341篇 |
2007年 | 338篇 |
2006年 | 310篇 |
2005年 | 242篇 |
2004年 | 247篇 |
2003年 | 199篇 |
2002年 | 198篇 |
2001年 | 146篇 |
2000年 | 126篇 |
1999年 | 110篇 |
1998年 | 52篇 |
1997年 | 43篇 |
1996年 | 40篇 |
1995年 | 32篇 |
1994年 | 36篇 |
1992年 | 85篇 |
1991年 | 87篇 |
1990年 | 81篇 |
1989年 | 68篇 |
1988年 | 74篇 |
1987年 | 56篇 |
1986年 | 42篇 |
1985年 | 66篇 |
1984年 | 55篇 |
1983年 | 46篇 |
1982年 | 30篇 |
1980年 | 34篇 |
1979年 | 42篇 |
1978年 | 46篇 |
1977年 | 36篇 |
1976年 | 34篇 |
1975年 | 29篇 |
1974年 | 43篇 |
1973年 | 33篇 |
1968年 | 31篇 |
排序方式: 共有8907条查询结果,搜索用时 125 毫秒
1.
Magnetic field influence on unsteady free convection flow of a second grade fluid near an infinite vertical flat plate with ramped wall temperature embedded in a porous medium is studied. It has been observed that magnitude of velocity as well as skin friction in case of ramped temperature is quite less than the isothermal temperature. Some special cases namely: (i) second grade fluid in the absence of magnetic field and porous medium and (ii) Newtonian fluid in the presence of magnetic field and porous medium, performing the same motion are obtained. Finally, the influence of various parameters is graphically shown. 相似文献
2.
3.
4.
5.
Perspective texture synthesis has great significance in many fields like video editing, scene capturing etc., due to its ability to read and control global feature information. In this paper, we present a novel example-based, specifically energy optimization-based algorithm, to synthesize perspective textures. Energy optimization technique is a pixel-based approach, so it’s time-consuming. We improve it from two aspects with the purpose of achieving faster synthesis and high quality. Firstly, we change this pixel-based technique by replacing the pixel computation with a little patch. Secondly, we present a novel technique to accelerate searching nearest neighborhoods in energy optimization. Using k- means clustering technique to build a search tree to accelerate the search. Hence, we make use of principal component analysis (PCA) technique to reduce dimensions of input vectors. The high quality results prove that our approach is feasible. Besides, our proposed algorithm needs shorter time relative to other similar methods. 相似文献
6.
M N Lorenzo R Y Khan Y Wang S C Tai G C Chan A H Cheung P A Marsden 《Biochimica et biophysica acta》2001,1522(1):46-52
Generation of the functionally pleiotropic members of the endothelin vasoactive peptide family is critically catalyzed by unique type II metalloproteases, termed endothelin converting enzymes (ECE). Isolation of human ECE-2 (EC 3.4.24.71) cDNAs revealed deduced open reading frames of 787 and 765 amino acids with approximately 60% identity with human ECE-1. Characterization of mRNA variants revealed mRNA structural diversity at the 5'-terminus. Two mRNA species exist containing distinct first and second exons. Furthermore, in one of these species, an in-frame deletion of the intracytoplasmic domain removed 29 amino acids. Because of the previously reported human genetic diseases ascribed to germline mutations of member genes of the endothelin family, ECE2 was localized in human chromosomes with fluorescence in situ hybridization and radiation hybrid mapping to 3q28-q29 and SHGC-20171/D3S1571, respectively. 相似文献
7.
A rapid, sensitive, assay for enzymes that degrade heparin is described. The procedure is based on the interference of heparin with color development during the interaction of protein with the dye Coomassie brilliant blue. The loss of this property when the glycosaminoglycan is degraded by heparinase can be used to quantify activity of the enzyme in pure form, or in complex biological samples such as tissue homogenates or serum. The assay is also suitable for studying dependence of heparinase activity under conditions such as varying pH and temperature. 相似文献
8.
Nimra Khan Dylan Pelletier Thomas S. McAlear Nathalie Croteau Simon Veyron Andrew N. Bayne Corbin Black Muneyoshi Ichikawa Ahmad Abdelzaher Zaki Khalifa Sami Chaaban Igor Kurinov Gary Brouhard Susanne Bechstedt Khanh Huy Bui Jean-François Trempe 《Structure (London, England : 1993)》2021,29(6):572-586.e6
9.
Wetlands Ecology and Management - 相似文献
10.
The mechanism of mass collaboration in risk management was studied during the Sichuan earthquake under a Web-based “PeopleFinder” project, where information is contributed and shared among mass contributors. The case study is provided by a great earthquake that happened in Wenchuan County, Sichuan Province, of southwestern China at 2:28 p.m. on May 12, 2008. We witnessed and experienced the rescue and relief efforts for the great earthquake. In this article, two fundamental frameworks are developed to study the mechanism of mass collaboration. Mass collaboration is proven to be effective in a big public crisis such as the Sichuan earthquake. 相似文献