全文获取类型
收费全文 | 4061篇 |
免费 | 177篇 |
国内免费 | 487篇 |
专业分类
化学 | 3282篇 |
晶体学 | 4篇 |
力学 | 344篇 |
综合类 | 75篇 |
数学 | 444篇 |
物理学 | 576篇 |
出版年
2024年 | 4篇 |
2023年 | 38篇 |
2022年 | 129篇 |
2021年 | 291篇 |
2020年 | 159篇 |
2019年 | 148篇 |
2018年 | 155篇 |
2017年 | 150篇 |
2016年 | 243篇 |
2015年 | 205篇 |
2014年 | 194篇 |
2013年 | 314篇 |
2012年 | 204篇 |
2011年 | 177篇 |
2010年 | 145篇 |
2009年 | 175篇 |
2008年 | 154篇 |
2007年 | 223篇 |
2006年 | 212篇 |
2005年 | 166篇 |
2004年 | 170篇 |
2003年 | 145篇 |
2002年 | 131篇 |
2001年 | 119篇 |
2000年 | 88篇 |
1999年 | 82篇 |
1998年 | 52篇 |
1997年 | 56篇 |
1996年 | 61篇 |
1995年 | 45篇 |
1994年 | 49篇 |
1993年 | 31篇 |
1992年 | 45篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 21篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 15篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有4725条查询结果,搜索用时 31 毫秒
21.
采用荧光法测定了辽河冷家油田冷47-556井特稠油乳化HLB值,然后以混合型表面活性剂、非离子型表面活性剂为主剂,快速渗透剂为辅剂按一定比例制备了水基降粘剂LJVR-1.实验结果表明,该降粘剂具有良好的乳化降粘性能,开采后易于破乳脱水,是一种较为理想的特稠油降粘剂. 相似文献
22.
A mapping from a subset of the real axis to a metric space with finite generalized variation is shown to admit extension to a mapping of the whole real axis with the same variation. This result leads to characterization of the generalized essential variation of a mapping. 相似文献
23.
Leda M. F. Gottschalk Ronaldo Nobrega Elba P. S. Bon 《Applied biochemistry and biotechnology》2003,108(1-3):799-807
The effect of aeration on lignin peroxidase production by Streptomyces viridosporus T7A was studied in a bench-scale bioreactor using a previously optimized growth medium (0.65% yeast extract and 0.1% corn
oil, pH7.0) at 37°C and natural pH. Airflow rates of 0.3, 1.0, and 1.5 vvm and a fixed agitation of 200 rpm were initially
studied followed by 1.0 vvm and 200, 300, 400, and 500 rpm. The use of 1.0 vvm and 400 rpm increased enzyme concentration
1.8-fold (100–180 U/L) and process productivity 4.8-fold (1.4–6.7 U/[L·h]) in comparison with the use of 200 rpm and 0.3 vvm.
The inexpensive corn oil, used as carbon source, besides its antifoam properties, proved to be nonrepressive for enzyme production. 相似文献
24.
Summary A new gas chromatographic method using an automatic purge-and-trap system coupled to a GC with mass selective detection to analyze styrene at the parts-per-trillions (ng kg–1) level is described. The method shows a good sensitivity and the detection limit is 10 ng kg–1 with a relative standard deviation (RSD) of 4.7% for 164 ng kg–1 styrene in olive oil. This analytical method has been successfully applied to the analysis of styrene in extra-virgin olive oil from the European market. 相似文献
25.
A quick sample preparation method was used for the determination of sulphur and trace metals in oil and oily products by the ICP with a minitorch. Stable aqueous emulsions of oils and oil products were made by using two kinds of emulsifiers (one with low sulphur content, the other sulfonated). Aqueous standard solutions can be used for the preparation of calibration solutions. The contents of S, Al, Cr, Cu, Fe, Mg, Ni and Pb in aqueous emulsions were determined and the results were in good agreement with the composition of oil standard solutions used for control analysis procedure. 相似文献
26.
L. G. Mezhlumyan Sh. Kh. Rakhimova P. Kh. Yuldashev N. K. Aikhodzhaeva M. A. Saidkhodzhaeva A. I. Massino S. Makhmudova 《Chemistry of Natural Compounds》2004,40(1):59-62
The glutelin fraction was used as the food value index of local corn. The base-soluble fraction was used as a test of the glassiness of local strains of rice grain. The content of gliadins and glutelins did not change over 24 h after wheat grain cultivated in Uzbekistan was moistened. 相似文献
27.
Qun Luo 《Journal of Global Optimization》2006,34(4):589-595
In the paper, by using Ky Fan’s section theorem, we obtain an existence theorem for vector equilibrium problems. Motivated
by the ideas of Kinoshita and McLennan, we introduce the concept of the essential component of the solution set for vector
equilibrium problems, and we prove that there exists at least one essential component of the solution set for every vector
equilibrium problem satisfying some conditions.
Research was partially supported by the Natural Science Foundation of Guangdong Province, P. R. China. 相似文献
28.
E. A. Sbrodova 《Mathematical Notes》2007,82(3-4):531-534
In this paper, we present an algorithm which, for a given compact orientable irreducible boundary irreducible 3-manifold M, verifies whether M contains an essential orientable surface (possibly, with boundary), whose genus is at most N. The algorithm is based on Haken’s theory of normal surfaces, and on a trick suggested by Jaco and consisting in estimating the mean length of boundary curves in an unknown essential surface of a given genus in the given manifold. 相似文献
29.
30.