全文获取类型
收费全文 | 127028篇 |
免费 | 8936篇 |
国内免费 | 16021篇 |
专业分类
化学 | 92758篇 |
晶体学 | 1761篇 |
力学 | 4236篇 |
综合类 | 1509篇 |
数学 | 17756篇 |
物理学 | 33965篇 |
出版年
2023年 | 1041篇 |
2022年 | 1773篇 |
2021年 | 3365篇 |
2020年 | 3107篇 |
2019年 | 3091篇 |
2018年 | 2666篇 |
2017年 | 3598篇 |
2016年 | 4015篇 |
2015年 | 3541篇 |
2014年 | 4828篇 |
2013年 | 9022篇 |
2012年 | 8034篇 |
2011年 | 7361篇 |
2010年 | 6312篇 |
2009年 | 8319篇 |
2008年 | 8488篇 |
2007年 | 8929篇 |
2006年 | 7752篇 |
2005年 | 6225篇 |
2004年 | 5784篇 |
2003年 | 4891篇 |
2002年 | 7226篇 |
2001年 | 3982篇 |
2000年 | 3492篇 |
1999年 | 3124篇 |
1998年 | 2864篇 |
1997年 | 2204篇 |
1996年 | 1684篇 |
1995年 | 1806篇 |
1994年 | 1629篇 |
1993年 | 1419篇 |
1992年 | 1376篇 |
1991年 | 928篇 |
1990年 | 778篇 |
1989年 | 695篇 |
1988年 | 583篇 |
1987年 | 467篇 |
1986年 | 454篇 |
1985年 | 513篇 |
1984年 | 429篇 |
1983年 | 264篇 |
1982年 | 472篇 |
1981年 | 604篇 |
1980年 | 542篇 |
1979年 | 581篇 |
1978年 | 473篇 |
1977年 | 351篇 |
1976年 | 295篇 |
1974年 | 110篇 |
1973年 | 182篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
高效液相色谱切换波长法测定油菜内源激素 总被引:1,自引:0,他引:1
采用反相高效液相色谱法(HPLC)切换波长法同时测定油菜中的内源激素赤霉素(GA3)、3-吲哚乙酸(IAA)和脱落酸(ABA),以甲醇:水:乙腈(20:60:20)为流动相,结果显示其检出限分别为GA3:0.08mg/L;IAA:0.015mg/L;ABA:0.025mg/L,比单波长检测的检出限提高了4-10倍;相对标准偏差(RSD)分别为GA3:6.3%,IAA:4.34%,ABA:7.95%.本实验采用切换波长法,显著减低了各组分的检出限,建立了一种以高灵敏度对多组分体系同时进行检测的方法.同时为快速、准确测定油菜内源激素提供了可靠方法. 相似文献
152.
meso-Tetra(n-hexyloxycarbonyl)porphyrin was found to be converted into porphine, the mother compound of porphyrins, in a 77% yield when heated in aqueous sulfuric acid at 180 °C over 30 min under an inert atmosphere. The observation demonstrates that the substituted porphyrin serves as a novel and useful precursor for porphine. 相似文献
153.
以酵母菌为脱氧剂,以透气性和透水气性好的聚乙烯醋酸乙烯酯(EVA)为基质,来制备一种新型的绿色脱氧包装膜。本文研究了EVA型号、脱氧剂含量、环境温度和湿度对这种脱氧膜的脱氧性能的影响。结果表明,这种新型的酵母菌脱氧膜有较好的脱氧性能,具有一定的市场应用前景。 相似文献
154.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
155.
156.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献
157.
158.
Let G=(V(G),E(G)) be a graph. A (n,G, λ)‐GD is a partition of the edges of λKn into subgraphs (G‐blocks), each of which is isomorphic to G. The (n,G,λ)‐GD is named as graph design for G or G‐decomposition. The large set of (n,G,λ)‐GD is denoted by (n,G,λ)‐LGD. In this work, we obtain the existence spectrum of (n,P3,λ)‐LGD. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 151–159, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10008 相似文献
159.
A simple simulation scheme that simultaneously describes the growth kinetics of SiO2 films at the nanometer scale and the SiOx/Si interface dynamics (its extent, and spatial/temporal evolution) is presented. The simulation successfully applies to experimental data in the region above and below 10 nm, reproduces the Deal and Grove linear-parabolic law and the oxide growth rate enhancement in the very thin film regime (the so-called anomalous region). According to the simulation, the oxidation is governed mainly by two processes: (a) the formation of a transition suboxide layer and (b) its subsequent drift towards the silicon bulk. We found that it is the superposition of these two processes that produces the crossover from the anomalous oxidation region behavior to the linear-parabolic law. 相似文献
160.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献