全文获取类型
收费全文 | 34059篇 |
免费 | 1158篇 |
国内免费 | 1065篇 |
专业分类
化学 | 14389篇 |
晶体学 | 361篇 |
力学 | 1731篇 |
综合类 | 56篇 |
数学 | 9582篇 |
物理学 | 10163篇 |
出版年
2023年 | 136篇 |
2022年 | 201篇 |
2021年 | 251篇 |
2020年 | 347篇 |
2019年 | 303篇 |
2018年 | 1441篇 |
2017年 | 1718篇 |
2016年 | 1032篇 |
2015年 | 905篇 |
2014年 | 793篇 |
2013年 | 1097篇 |
2012年 | 3622篇 |
2011年 | 2793篇 |
2010年 | 2165篇 |
2009年 | 1887篇 |
2008年 | 905篇 |
2007年 | 886篇 |
2006年 | 872篇 |
2005年 | 4662篇 |
2004年 | 4092篇 |
2003年 | 2423篇 |
2002年 | 624篇 |
2001年 | 388篇 |
2000年 | 188篇 |
1999年 | 265篇 |
1998年 | 145篇 |
1997年 | 110篇 |
1996年 | 80篇 |
1995年 | 73篇 |
1994年 | 53篇 |
1993年 | 49篇 |
1992年 | 191篇 |
1991年 | 168篇 |
1990年 | 146篇 |
1989年 | 116篇 |
1988年 | 117篇 |
1987年 | 61篇 |
1986年 | 56篇 |
1985年 | 52篇 |
1984年 | 39篇 |
1979年 | 40篇 |
1976年 | 86篇 |
1975年 | 44篇 |
1974年 | 45篇 |
1973年 | 53篇 |
1972年 | 41篇 |
1970年 | 35篇 |
1969年 | 38篇 |
1968年 | 36篇 |
1966年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
21.
Sándor G?r?g 《Analytical sciences》2004,20(5):767-782
The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis. 相似文献
22.
The electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols on graphite electrodes was studied using cyclic voltammetry, chronoamperometry, constant-potential coulometry and preparative constant-potential electrolysis techniques. The data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro disc Pt-electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The compounds were subjected to constant-potential preparative electrolysis and the electrolysis products were purified and identified by spectroscopic methods. Based on these findings, a mechanism for the electro-reduction process is proposed. 相似文献
23.
溶胶-凝胶法制备小颗粒(Y,Gd)BO_3∶Eu及其表征 总被引:1,自引:0,他引:1
用溶胶 凝胶方法制备了平均粒径为 1~ 2 μm的小颗粒、高发射效率的 (Y ,Gd)BO3 ∶Eu红色发射荧光体。用XRD、SEM、粒度分析和PL光谱对荧光体作了表征和研究。常规固相反应合成 (Y ,Gd)BO3 ∶Eu需在 1 2 0 0℃以上才能形成均一的固溶体。而溶胶 凝胶法制取稀土正硼酸盐 80 0℃灼烧已可形成均一的单相 (Y ,Gd)BO3 ∶Eu,在 1 1 0 0℃可得到发光亮度最高的荧光体。它的亮度是常规固相反应于 1 2 0 0℃制得的荧光体的 1 2 0 %。采用溶胶 凝胶法制取 (Y ,Gd)BO3 ∶Eu荧光体 ,可在相当宽的实验条件范围内得到小粒径、窄分布和高亮度的荧光体 ,且有良好的颗粒形貌。 相似文献
24.
JingXiaWANG ChengYouKAN DeShanLIU 《中国化学快报》2004,15(10):1161-1163
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA. 相似文献
25.
WeiMinSHI JianWU YiFengWU KaiXianQIAN 《中国化学快报》2004,15(12):1427-1429
A mono-funtionalised tetraphenylporphyrin (TPP) bearing valine moiety at the phenyl ring was synthesized for photocytotoxicity examination in four steps, starting from regiospecific mono-nitration of TPP at the phenyl ring. The in vitro photocytotoxicitic effect against SPC-Al adenocarcinona cell line was tested. 相似文献
26.
27.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents. 相似文献
28.
29.
30.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help. 相似文献