全文获取类型
收费全文 | 34073篇 |
免费 | 225篇 |
国内免费 | 292篇 |
专业分类
化学 | 14232篇 |
晶体学 | 278篇 |
力学 | 1441篇 |
综合类 | 12篇 |
数学 | 9963篇 |
物理学 | 8664篇 |
出版年
2020年 | 67篇 |
2018年 | 1223篇 |
2017年 | 1468篇 |
2016年 | 788篇 |
2015年 | 634篇 |
2014年 | 554篇 |
2013年 | 800篇 |
2012年 | 3257篇 |
2011年 | 2512篇 |
2010年 | 1896篇 |
2009年 | 1622篇 |
2008年 | 749篇 |
2007年 | 796篇 |
2006年 | 786篇 |
2005年 | 4647篇 |
2004年 | 4081篇 |
2003年 | 2452篇 |
2002年 | 645篇 |
2001年 | 362篇 |
2000年 | 175篇 |
1999年 | 236篇 |
1998年 | 162篇 |
1997年 | 142篇 |
1996年 | 106篇 |
1995年 | 113篇 |
1994年 | 90篇 |
1993年 | 75篇 |
1992年 | 238篇 |
1991年 | 196篇 |
1990年 | 202篇 |
1989年 | 145篇 |
1988年 | 162篇 |
1987年 | 125篇 |
1986年 | 88篇 |
1985年 | 137篇 |
1984年 | 92篇 |
1983年 | 88篇 |
1982年 | 93篇 |
1981年 | 84篇 |
1979年 | 103篇 |
1978年 | 95篇 |
1977年 | 73篇 |
1976年 | 158篇 |
1975年 | 115篇 |
1974年 | 97篇 |
1973年 | 99篇 |
1972年 | 82篇 |
1970年 | 84篇 |
1967年 | 69篇 |
1966年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 14 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.
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
24.
On a Definitizable Analog of the Trigonometric Moment Problem Generating an Indefinite Toeplitz Form
We prove the existence of an integro-polynomial representation for a sequence of numbers such that there exists a difference operator mapping this sequence to a sequence that generates the solvable trigonometric moment problem. A similar result related to the power moment problem was given in [12]. 相似文献
25.
26.
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
27.
28.
Entropy analysis and wavelet transforms are used to study the Southern Oscillation index (SOI) and multivariate ENSO index (MEI) indexes for the El Niño–Southern Oscillation. Trends to large decreasing symbolic chains responsible for La Niña and interrupted increasing chains for El Niño are found in the MEI persistence series. These are all located in regions where the wavelet transforms of both indexes reveal the existence of mid-range correlations. The SOI and MEI indexes are mutually correlated in a non-trivial manner in the time. 相似文献
29.
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
30.
S. Trebert Haeberlin F. Lux J. Karl T. Spruss H. Schönenberger 《Journal of Radioanalytical and Nuclear Chemistry》1987,113(2):461-467
As part of an examination of the cytostatic effects of 1,2-diarylethylenediamine-platinum(II)-complexes the contents of platinum and biologically essential trace elements of tumour tissue and different organs were determined. The activation analysis procedure — separation of32P, isolation of199Au and99Mo — is described. In the course of a pharmakokinetical experiment with tumourbearing rats (DMBA induced hormone-dependent tumours) the desired enrichment of the administered drug in the tumour tissue was found. Changes of the trace element level of tumour tissue were found for hormone-dependent MXT-mammary tumours on mice. 相似文献