全文获取类型
收费全文 | 29507篇 |
免费 | 131篇 |
国内免费 | 281篇 |
专业分类
化学 | 10904篇 |
晶体学 | 267篇 |
力学 | 1403篇 |
综合类 | 12篇 |
数学 | 9070篇 |
物理学 | 8263篇 |
出版年
2021年 | 37篇 |
2020年 | 33篇 |
2019年 | 49篇 |
2018年 | 1197篇 |
2017年 | 1448篇 |
2016年 | 727篇 |
2015年 | 576篇 |
2014年 | 494篇 |
2013年 | 692篇 |
2012年 | 3164篇 |
2011年 | 2337篇 |
2010年 | 1815篇 |
2009年 | 1552篇 |
2008年 | 587篇 |
2007年 | 637篇 |
2006年 | 622篇 |
2005年 | 4455篇 |
2004年 | 3934篇 |
2003年 | 2321篇 |
2002年 | 503篇 |
2001年 | 294篇 |
2000年 | 95篇 |
1999年 | 186篇 |
1998年 | 113篇 |
1997年 | 83篇 |
1996年 | 56篇 |
1995年 | 47篇 |
1994年 | 52篇 |
1993年 | 36篇 |
1992年 | 173篇 |
1991年 | 156篇 |
1990年 | 136篇 |
1989年 | 113篇 |
1988年 | 101篇 |
1987年 | 62篇 |
1986年 | 44篇 |
1985年 | 45篇 |
1984年 | 35篇 |
1979年 | 43篇 |
1978年 | 33篇 |
1976年 | 91篇 |
1975年 | 47篇 |
1974年 | 46篇 |
1973年 | 54篇 |
1972年 | 42篇 |
1970年 | 38篇 |
1969年 | 41篇 |
1968年 | 38篇 |
1967年 | 33篇 |
1966年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
I Cserpan M Kalman M L Tj?rnhammar A Simoncsits 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(3):265-272
A general method to convert single-stranded, chemically synthesized oligonucleotides into cloned duplexes is described. Oligonucleotides supplied with 3'-terminal extensions that are complementary to 3'-protruding ends obtained by certain restriction enzymes can be cloned either directly or with the help of an adapter molecule into double-stranded vectors. Two methods have also been developed for consecutive cloning applications. According to these methods, the synthetic oligonucleotides (and their enzymatically prepared complementary strands) are joined, one after the other, inside a cloning vector, each joining requiring one cloning step. Synthetic genes are thus built up from oligonucleotides corresponding to only one strand of the DNA. The sequential assembly of the cloned duplex takes place in the 5' to 3' direction. Each oligonucleotide is supplied with a four-nucleotide-long 3'-terminal extension, but this sequence is eliminated when the joining takes place, leaving no limiting sequence between the oligonucleotides. The two consecutive cloning methods, the adapter and the polycloning site methods, are illustrated by the assembly of short artificial genes. 相似文献
62.
Sam I. Ahonkhai
Andreas N
llePeter Behr
Horst Heydtmann 《Journal of photochemistry and photobiology. A, Chemistry》1994,80(1-3):389-392Experimental results are presented of a Fourier transform IR product study at 298 K of the reaction system CFO+O2 at oxygen pressures between 3 and 250 mbar. Pulsed photolysis of oxalyl fluoride (CFO)2 or formyl fluoride (CHFO) at 193 nm was used to produce CFO. As stable products we detected bis-fluoroformyl peroxide, carbonyl fluoride and carbon dioxide. The yields of the peroxide and of CF2O were measured as a function of [O2]/[precursor] and are discussed qualitatively. 相似文献
63.
Andrzej Wi?nicki 《Journal of Mathematical Analysis and Applications》2002,267(1):158-172
We use a newly introduced concept of neocompactness to study problems from metric fixed point theory. In particular, we give a sufficient condition for a superreflexive Banach space X to have the fixed point property and obtain shorter proofs of some well-known results in that theory. 相似文献
64.
65.
Sam Lohse 《Microchemical Journal》2006,82(1):66-72
Although photooxidation has previously been shown to be successful in removing organic contaminants from water, methods combining the rapid photooxidation of the desired contaminant with easy catalyst manipulation and removal are few and far between. In the absence of an easy means of catalyst removal, the photooxidation process becomes more costly and time consuming, and photocatalysis cannot be employed as an in situ method for the remediation of aqueous organic contaminants. In this study, the photocatalyst was added to an aqueous trichloroethylene (TCE) solution in the form of TiO2-coated buoyant microspheres. The solution, placed in a flow-cell photoreactor along with the buoyant catalyst, was irradiated with a UV-filtered Xenon light source. Limited sample sizes necessitated the development of a low-cost headspace GC/MS analysis method, utilizing a standard direct-injection autosampler. This analytical technique aptly monitored reaction progress and indicated that aqueous TCE concentration decreases by nearly 90% in the first hour of irradiation. Subsequent solvent extraction GC/MS analysis indicated that the TCE is initially sorbed by the photocatalyst spheres, but as irradiation continued, TCE is removed from the catalyst spheres surfaces. During the course of irradiation, the expected TCE mineralization product hydrochloric acid appeared, as indicated by a decrease in pH and ion chromatography analysis. The microsphere-born catalyst was easily removed from the treated solution by filtration. Thus, it is possible that a method for effective, low-cost in situ photooxidation of aqueous organic contaminants will be realized in the near future. 相似文献
66.
In vitro and in vivo proton T1 data are reported that demonstrate that the paramagnetic copper-D-penicillamine complex can be applied as a potential contrast agent to magnetic resonance imaging. 相似文献
67.
T Christensen E B Jensen F Junker H Dalb?ge F Abildgaard J J Led 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1992,46(1):97-99
Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized. 相似文献
68.
L Jirovetz G Buchbauer W J?ger A Woidich A Nikiforov 《Biomedical chromatography : BMC》1992,6(3):133-134
After inhalation experiments with sandalwood oil and the pure fragrance compounds coumarin and alpha-terpineol, substances were detected and measured in the blood samples of test animals (mice) using gas chromatography/mass spectrometry (GC/MS) (MID) in connection with GC/FTIR (SWC), GC/AES (carbon and oxygen trace) and flame ionization detection/gas chromatography. Using tiglinic acid benzyl ester as the internal standard the following concentrations in serum could be found: alpha-santalol 6.1 ng/mL, beta-santalol 5.3 ng/mL and alpha-santalene 0.5 ng/mL. In separate inhalation experiments with coumarin and with alpha-terpineol the corresponding concentrations were 7.7 ng/mL and 6.9 ng/mL, respectively. 相似文献
69.
Adducts of the conjugate addition of benzylamine to enantiopure amides of aroylacrylic acid possess high enantiomeric and diastereomeric purity. A high degree of stereoselectivity has been achieved by means of crystallization-induced asymmetric transformation. A practical synthesis leading to dipeptides containing homophenylalanine is depicted. 相似文献
70.
It is shown that in-situ
166mHo (I = 7) in a spherical single crystal of HoF3 can be used as sensitive internal thermometer to thermally detect NMR (NMR-TDNO) from the 100% abundant stable 165Ho (I = 7/2) nuclei. In addition, new 166mHo NMRON results are reported. Both the 166mHo NMRON and 165Ho NMR-TDNO spectra show three distinct quadrupolar split sub-resonances, in zero applied field. The data is used to make
estimates of the Ho magnetic moments and quadrupole parameters for the 166mHo and 166mHo sites. 相似文献