全文获取类型
收费全文 | 3279篇 |
免费 | 107篇 |
专业分类
化学 | 1795篇 |
晶体学 | 43篇 |
力学 | 94篇 |
数学 | 699篇 |
物理学 | 755篇 |
出版年
2023年 | 22篇 |
2022年 | 38篇 |
2021年 | 55篇 |
2020年 | 65篇 |
2019年 | 48篇 |
2018年 | 105篇 |
2017年 | 87篇 |
2016年 | 136篇 |
2015年 | 99篇 |
2014年 | 135篇 |
2013年 | 249篇 |
2012年 | 162篇 |
2011年 | 214篇 |
2010年 | 123篇 |
2009年 | 122篇 |
2008年 | 114篇 |
2007年 | 125篇 |
2006年 | 94篇 |
2005年 | 99篇 |
2004年 | 74篇 |
2003年 | 61篇 |
2002年 | 63篇 |
2001年 | 37篇 |
2000年 | 41篇 |
1999年 | 36篇 |
1998年 | 35篇 |
1997年 | 27篇 |
1996年 | 41篇 |
1994年 | 29篇 |
1993年 | 24篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 21篇 |
1985年 | 30篇 |
1983年 | 24篇 |
1982年 | 24篇 |
1981年 | 22篇 |
1980年 | 31篇 |
1979年 | 24篇 |
1978年 | 35篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 33篇 |
1974年 | 28篇 |
1969年 | 23篇 |
1968年 | 24篇 |
1966年 | 22篇 |
排序方式: 共有3386条查询结果,搜索用时 15 毫秒
111.
A new, sensitive spectrophotometric determination of palladium has been developed, based on the extraction of the red Pd(II) chelate with 4-(2-pyridylazo)resorcinol in the presence of N,N′-diphenylguanidine into n-butanol; the sensitivity of the method according to Sandell is S = 1.12 μg cm?2, ?530 = 9.4 × 104 liters mol?1 cm?1, and palladium can be determined at concentrations from 0.21 to 1.91 μg ml?1. 相似文献
112.
E.?A.?CastroEmail author A.?P.?Toropova A.?A.?Toropov D.?V.?Mukhamedjanova 《Structural chemistry》2005,16(3):305-324
We examine the encoding of chemical structure of organic compounds by Labeled Hydrogen-Filled Graphs (LHFGs). Quantitative Structure-Property Relationships (QSPR) for a representative set of 150 organic molecules have been derived by means of the optimization of correlation weights of local invariants of the LHFGs. We have tested as local invariants Morgan extended connectivity of zero- and first order, numbers of path of length 2 (P2) and valence shells of distance of 2 (S2) associated with each atom in the molecular structure, and the Nearest Neighboring Codes (NNC). The best statistical characteristics for the Gibbs free energy has been obtained for the NNC weighting. Statistical parameters corresponding to this model are the following n = 100, r2 = 0.9974, s = 5.136 kJ/mol, F = 38319 (training set); n = 50, r2 = 0.9990, s = 3.405 kJ/mol, F = 48717 (test set). Some possible further developments are pointed out. 相似文献
113.
7-deaza-2,8-diaza-2'-deoxyadenosine (4) was synthesized from 8-aza-7-deaza-2'-deoxyadenosine (1) via the 1,N(6)-etheno derivative 5. Ring opening with sodium hydroxide followed by ring closure in the presence of sodium nitrite formed the tricyclic intermediate 5 from which the transiently introduced "etheno" moiety was removed with NBS. Compound 4 was converted to the phosphoramidite 11, which was employed in solid-phase oligonucleotide synthesis. Base pairing studies on 4, incorporated in a 12-mer duplex, showed that this adenine nucleoside analogue forms a strong base pair with dG but not with dT. This novel base pair is as stable as that of the canonical dA-dT pair. As a result of the absence of nitrogen-7 compound 4 is expected to form a face to face base pair with dG. 相似文献
114.
Prof. Dr. Fritz Sauter Peter Stanetty Hans Potužak Morteza Baradar 《Monatshefte für Chemie / Chemical Monthly》1976,107(3):669-673
The title substances1 and2 were prepared by acylation of the corresponding ethyl 2-amino-thiophene- (or:-4,5,6,7-tetrahydro-benzo[b]thiophene)-3-carboxylates, in some cases followed by reactions introducing a basic substituent.Additionally a group of 2-aroylamino-thiophene-(or:-4,5,6,7-tetrahydro-benzo[b]thiophene)-3-carboxamides was subjected to ring closure reactions, yielding the corresponding 2-aryl-thieno[2,3-d]pyrimidin-4(3H)-ones and 2-aryl-[1]benzothieno[2,3-d]pyrimidin-4(3H)-ones (both:3).
Zum Teil unter Mitarbeit vonFerdinand Fuhrmann 相似文献
Zum Teil unter Mitarbeit vonFerdinand Fuhrmann 相似文献
115.
106Ru chloro and nitrosyl-nitrato complexes in sea water were separated into several species by continuous electrophoresis on
a filter paper curtain. Biological uptake experiments were carried out on sea algae Fucus virsoides with fractionated106Ru chloro and nitrosyl-nitrato complex species in sea water. The biological uptake of106Ru chloro complex species was about 8 times higher than the uptake of106Ru nitrosyl-nitrato species. Electrophoretically most mobile electrically positively charged cationic species in both systems
also showed about 8 times higher biological uptake than the most mobile negatively charged anionic species. A close relation
of the biological uptake to the sign of the electrical charge and the electrophoretic mobility of the species is demonstrated.
The results are discussed with respect to possible danger to the biological environment as a consequence of the aging of ruthenium
species in sea water resulting from106Ru waste disposal to the sea from a nuclear reprocessing plant.
On leave of absence from the National Institute of Radiological Sciences, 9-1, 4-chome, Anagawa, Chiba-shi, Japan, on a fellowship
from The Science and Technology Agency of the Japanese Govemment. 相似文献
116.
The stability of poly(N-methylaniline) (PNMA) as electrode material has been studied in aqueous solutions of sulfuric acid with the use of electrochemical
and in situ Raman spectroscopic techniques. It has been shown that the electrochemical decomposition of electrodeposited PNMA
films follows a first-order reaction kinetics. The decomposition rate constants vary between 1.2 × 10−5 and 2.0 × 10−3 s−1 for electrode potential varying between 0.2 and 1.0 V vs Ag/AgCl, respectively. In situ Raman spectroscopy has been applied
in obtaining kinetic data at selected electrode potentials, and good correlation of these data with the corresponding data
obtained by cyclic voltammetry has been found. As compared to polyaniline, the decomposition of PNMA proceeds at nearly the
same rate at electrode potentials not exceeding 0.5 V. The decomposition of PNMA proceeds faster within the potential limits
of 0.5 to 0.8 V and slower at electrode potentials exceeding 0.8 V as compared to polyaniline.
This article is dedicated to Professor Algirdas Vaškelis (Institute of Chemistry, Vilnius, Lithuania) on the occasion of his
70th birthday and in honour of his contributions to electrochemistry and physical chemistry. 相似文献
117.
Zusammenfassung 1,3-Dimethyl-4,5-diaminouracil (DAL) hat sich als sehr empfindliches Reagens zum selektiven Nachweis von Co2+-Ionen im stark alkalischen Medium einer Phosphatpufferlösung (pH=11,20) erwiesen. Es wurden vier Additionsverbindungen von DAL mit den Zentralatomen Cd(II), Pd(II), Ni(II) und Co(II) im Verhältnis Me DAL=1 2 hergestellt. Spektrophotometrische Untersuchungen weisen darauf hin, daß bei pH 6 bis 7 eine Komplexverbindung im Verhältnis CoDAL=12 gebildet wird.
Summary 1,3-dimethyl-4,5-diaminouracil (DAL) has been found to be a very sensitive reagent for the selective detection of Co2+ ions in strong alkaline medium of a phosphate buffer solution (pH=11.20). Four addition compounds of DAL with the central atoms Cd(II), Pd(II), Ni(II) and Co(II) with the ratio MeDal=12 have been prepared. Spectrophotometric studies indicate that at pH=6–7, complex compound is produced with the ratio CoDAL=12.相似文献
118.
119.
120.