全文获取类型
收费全文 | 97306篇 |
免费 | 3580篇 |
国内免费 | 3054篇 |
专业分类
化学 | 38816篇 |
晶体学 | 1048篇 |
力学 | 7752篇 |
综合类 | 172篇 |
数学 | 34231篇 |
物理学 | 21921篇 |
出版年
2024年 | 75篇 |
2023年 | 422篇 |
2022年 | 723篇 |
2021年 | 747篇 |
2020年 | 863篇 |
2019年 | 864篇 |
2018年 | 10949篇 |
2017年 | 10709篇 |
2016年 | 6972篇 |
2015年 | 1821篇 |
2014年 | 1493篇 |
2013年 | 1853篇 |
2012年 | 5498篇 |
2011年 | 12157篇 |
2010年 | 6858篇 |
2009年 | 7076篇 |
2008年 | 7770篇 |
2007年 | 9815篇 |
2006年 | 1290篇 |
2005年 | 2224篇 |
2004年 | 2251篇 |
2003年 | 2583篇 |
2002年 | 1713篇 |
2001年 | 838篇 |
2000年 | 699篇 |
1999年 | 550篇 |
1998年 | 524篇 |
1997年 | 444篇 |
1996年 | 494篇 |
1995年 | 360篇 |
1994年 | 320篇 |
1993年 | 290篇 |
1992年 | 215篇 |
1991年 | 224篇 |
1990年 | 169篇 |
1989年 | 178篇 |
1988年 | 154篇 |
1987年 | 113篇 |
1986年 | 105篇 |
1985年 | 109篇 |
1984年 | 96篇 |
1983年 | 70篇 |
1982年 | 71篇 |
1981年 | 57篇 |
1980年 | 64篇 |
1979年 | 52篇 |
1978年 | 45篇 |
1914年 | 46篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
13.
C Z Shi Z Y Zhang L Z Zhuang 《Science in China. Series B, Chemistry, life sciences & earth sciences》1991,34(9):1098-1104
The effect of hormones on progesterone secretion by 6-8 week human trophoblast tissue cultured in serum-free medium has been investigated. GnRH at low concentration (10(-10)-10(-8) mol/L) stimulated progesterone secretion, while high dose (10(-6)-10(-5) mol/L) produced inhibitory effect. The progesterone secretion could be significantly decreased by addition of anti-hCG antiserum or monoclonal anti-hCG IgG in a dose- and time-dependent manner. Various concentrations of TRH, PGE2, PGF2 alpha, testosterone and estradiol were found to be ineffective. These data indicate clearly that progesterone production by human trophoblast tissue at early gestation stage is under the modulation of GnRH and hCG. 相似文献
14.
15.
16.
17.
James Tanton 《Mathematical Intelligencer》2007,29(3):55-59
This column is a place for those bits of contagious mathematics that travel from person to person in the community, because
they are so elegant, suprising, or appealing that one has an urge to pass them on.
Contributions are most welcome. 相似文献
18.
铸膜液的溶剂体系(溶剂和非溶剂)对不对称膜形态的形成有重要作用。为了探索溶剂和透气性间的关系,本文考虑到了制备BCA梯度密度不对称膜的各种溶剂的一系列物理参数,得到了一些定性结果,并指出了更全面、明确、解释两者关系的研究方向。 相似文献
19.
Lingsheng Shi 《Journal of Graph Theory》2005,50(3):175-185
The Ramsey number R(G1,G2) of two graphs G1 and G2 is the least integer p so that either a graph G of order p contains a copy of G1 or its complement Gc contains a copy of G2. In 1973, Burr and Erd?s offered a total of $25 for settling the conjecture that there is a constant c = c(d) so that R(G,G)≤ c|V(G)| for all d‐degenerate graphs G, i.e., the Ramsey numbers grow linearly for d‐degenerate graphs. We show in this paper that the Ramsey numbers grow linearly for degenerate graphs versus some sparser graphs, arrangeable graphs, and crowns for example. This implies that the Ramsey numbers grow linearly for degenerate graphs versus graphs with bounded maximum degree, planar graphs, or graphs without containing any topological minor of a fixed clique, etc. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
20.
The rate of nucleophilic substitution at the phosphorus centre of dialkyl methylphosphonates by methoxide and ethoxide has been studied to investigate the possible involvement of hexacoordinated phosphorus species in this reaction. For alkoxide concentrations less than ca. 1.5 M the rate increases with the square of alkoxide concentration. However, consideration of the activity of the alkoxides, represented by an appropriate acidity function, reveals that only one equivalent of alkoxide is involved in the rate-determining step. Thus, there is no requirement to invoke the intermediacy of a hexacoordinated species in the reaction pathway. © John Wiley & Sons, Inc. 相似文献