全文获取类型
收费全文 | 6153篇 |
免费 | 477篇 |
国内免费 | 286篇 |
专业分类
化学 | 4163篇 |
晶体学 | 76篇 |
力学 | 202篇 |
综合类 | 31篇 |
数学 | 799篇 |
物理学 | 1645篇 |
出版年
2023年 | 69篇 |
2022年 | 148篇 |
2021年 | 142篇 |
2020年 | 189篇 |
2019年 | 176篇 |
2018年 | 132篇 |
2017年 | 134篇 |
2016年 | 211篇 |
2015年 | 197篇 |
2014年 | 227篇 |
2013年 | 313篇 |
2012年 | 415篇 |
2011年 | 473篇 |
2010年 | 267篇 |
2009年 | 228篇 |
2008年 | 378篇 |
2007年 | 352篇 |
2006年 | 342篇 |
2005年 | 282篇 |
2004年 | 238篇 |
2003年 | 210篇 |
2002年 | 151篇 |
2001年 | 104篇 |
2000年 | 95篇 |
1999年 | 88篇 |
1998年 | 68篇 |
1997年 | 63篇 |
1996年 | 77篇 |
1995年 | 69篇 |
1994年 | 60篇 |
1993年 | 56篇 |
1992年 | 63篇 |
1991年 | 39篇 |
1990年 | 33篇 |
1989年 | 39篇 |
1988年 | 35篇 |
1987年 | 28篇 |
1985年 | 58篇 |
1984年 | 29篇 |
1983年 | 34篇 |
1982年 | 51篇 |
1981年 | 44篇 |
1980年 | 34篇 |
1979年 | 42篇 |
1978年 | 44篇 |
1977年 | 46篇 |
1976年 | 36篇 |
1975年 | 33篇 |
1974年 | 49篇 |
1973年 | 32篇 |
排序方式: 共有6916条查询结果,搜索用时 15 毫秒
991.
R Bonfiglio RC King TV Olah K Merkle 《Rapid communications in mass spectrometry : RCM》1999,13(12):1175-1185
A post-column infusion system was developed in order to analyze suppression of electrospray ionization (ESI) tandem mass spectrometry response in the presence of endogenous plasma interferences. By enabling direct detection of these interfering components, this experimental system was used to analyze the ability of several common extraction procedures to remove endogenous plasma components that cause changes in the ESI response of model drug substances. Methyl-t-butyl ether (MTBE) liquid-liquid, Oasis and Empore solid-phase, and acetonitrile (ACN) protein precipitation sample preparation methods were tested using the post-column infusion system. In all cases, ACN protein precipitation samples showed the greatest amount of ESI response suppression while liquid-liquid extracts demonstrated the least. In addition, the three test compounds, phenacetin, caffeine, and a representative Merck compound, demonstrated that ESI response suppression is compound dependent. Suppression was greatest with caffeine, the most polar analyte, and the smallest for the Merck compound, the least polar analyte. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
992.
To improve the productivities of an automated container terminal, it is important to schedule different types of handling
equipment in an integrated way. A mixed-integer programming model, which considers various constraints related to the integrated
operations between different types of handling equipment, is formulated. A heuristic algorithm, called multi-layer genetic
algorithm (MLGA) is developed with a view to overcome the computation difficulty for solving the mathematical model. A numerical
experimentation is carried out in order to evaluate the performance of the algorithm. 相似文献
993.
By the comparison of the reaction products of gem-dihalocyclopropanes under various conditions, it is suggested that similar to the reactions with metals, the reactive radical intermediates which make the reaction results complicated are formed in the reactions of gem-dihalocyclopropanes with alkyl lithium. Studies on the competitions between ring opening and intramolecular C—H insertions of cyclopropylidenes generated by the reactions of gem-dihalocyclopropanes with metals and discussions on the reaction mechanism are also given in this paper. 相似文献
994.
995.
996.
Jonathan King 《Israel Journal of Mathematics》1987,59(3):377-380
If transformationR is ap-point extension of a mixingT thenp · rank(T) lower bounds the rank ofR.
The author was partially supported by NSF grant DMS8501519. 相似文献
997.
For positive integers s and k1,k2,…,ks, the van der Waerden number w(k1,k2,…,ks;s) is the minimum integer n such that for every s-coloring of set {1,2,…,n}, with colors 1,2,…,s, there is a ki-term arithmetic progression of color i for some i. We give an asymptotic lower bound for w(k,m;2) for fixed m. We include a table of values of w(k,3;2) that are very close to this lower bound for m=3. We also give a lower bound for w(k,k,…,k;s) that slightly improves previously-known bounds. Upper bounds for w(k,4;2) and w(4,4,…,4;s) are also provided. 相似文献
998.
Self-Affine Sets and Graph-Directed Systems 总被引:1,自引:0,他引:1
Abstract. A self-affine set in R
n
is a compact set T with A(T)= ∪
d∈ D
(T+d) where A is an expanding n× n matrix with integer entries and D
={d
1
, d
2
,···, d
N
} ⊂ Z
n
is an N -digit set. For the case N = | det(A)| the set T has been studied in great detail in the context of self-affine tiles. Our main interest in this paper is to consider the
case N > | det(A)| , but the theorems and proofs apply to all the N . The self-affine sets arise naturally in fractal geometry and, moreover, they are the support of the scaling functions in
wavelet theory. The main difficulty in studying such sets is that the pieces T+d, d∈ D, overlap and it is harder to trace the iteration. For this we construct a new graph-directed system to determine whether
such a set T will have a nonvoid interior, and to use the system to calculate the dimension of T or its boundary (if T
o
≠ ). By using this setup we also show that the Lebesgue measure of such T is a rational number, in contrast to the case where, for a self-affine tile, it is an integer. 相似文献
999.
Hongji Liu Byung-Yun Cho Richard Strong Ira S. Krull Steven Cohen King C. Chan Haleem J. Issaq 《Analytica chimica acta》1999,400(1-3):181-209
Peptides and small proteins, of limited molecular weight (MW) can be derivatized with a 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (6-AQC) reagent, leading to a single capillary zone electrophoresis (CZE) peak, suggestive of a completely tagged product. The number of tags per molecule was demonstrated by matrix assisted, laser desorption, time-of-flight mass spectrometry (MALDI-TOFMS) studies. In CZE, these species have greatly improved plate count and peak shape, improved (lowered) detectabilities, and in general, improved identification properties in the CZE mode in high performance capillary electrophoresis (HPCE). The formation of what appears to be a single, homogeneously tagged product is a function of how the derivatizations are performed. Once these conditions are optimized, virtually all peptides and small proteins tested (limited MW) can form single, fully tagged products, with the desirable CZE properties. These derivatization approaches thus lead to products that perform and are detected much better in CZE than their precursors (native, untagged peptides). The determined plate counts for these tagged peptides were as high as 6 million plates/m, which was very reproducible, and 59–12,000 times higher than the untagged (native) molecules. The peak symmetry was also improved greatly. The limit of detection (LOD) of some tested 6-AQC tagged peptides were nine to 209 times improved (lower) with ultraviolet (UV) absorption detection, again as compared with that for the native species. The LOD could be further lowered via laser induced fluorescence (LIF) detection in CZE, especially when acetonitrile (ACN) containing buffers were used. 相似文献
1000.