全文获取类型
收费全文 | 1104篇 |
免费 | 25篇 |
国内免费 | 7篇 |
专业分类
化学 | 663篇 |
晶体学 | 8篇 |
力学 | 79篇 |
数学 | 138篇 |
物理学 | 248篇 |
出版年
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 60篇 |
2012年 | 48篇 |
2011年 | 52篇 |
2010年 | 25篇 |
2009年 | 31篇 |
2008年 | 47篇 |
2007年 | 67篇 |
2006年 | 58篇 |
2005年 | 50篇 |
2004年 | 27篇 |
2003年 | 38篇 |
2002年 | 38篇 |
2001年 | 18篇 |
2000年 | 31篇 |
1999年 | 16篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 18篇 |
1992年 | 25篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 19篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1983年 | 17篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 27篇 |
1976年 | 8篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 12篇 |
1972年 | 10篇 |
1968年 | 8篇 |
1967年 | 6篇 |
排序方式: 共有1136条查询结果,搜索用时 359 毫秒
21.
S. S. Krishnamurthy P. Ramabrahmam A. R. Vasudeva Murthy R. A. Shaw M. Woods 《无机化学与普通化学杂志》1985,522(3):226-234
The reactions of pentachloro(2′, 2′, 2′-triphenylphosphazen-1′-yl)cyclotriphosphazene, N3P3Cl5(NPPh3), with primary and secondary amines have been investigated using diethyl ether, methyl cyanid or benzene as the solvent. The structures of the products obtained, N3P3Cl5minus;nRn(NPPh3) [n = 1, R = NHMe, NHBut, NMe2, NC5H10, NEt2; n = 2, R = NMe2, NC5H10, NEt2; n = 3, R = NMe2, NHBut; n = 5, R = NMe2] are elucidated by 1H and 31P NMR spectroscopy. The ? NPPh3 substituent exerts a pronounced geminal directing influence on incoming secondary amino nucleophiles; compounds containing a ≡ PCl(NPPh3) group are not formed at the bis and subsequent stages of chlorine replacement. The reactions that involve primary amines follow the pattern established for the analogous reactions of hexachlorocyclotriphosphazene. The effect of solvent and possible mechanism(s) are discussed. 相似文献
22.
We have used a micro-gel system to analyze the proteins in extracts of amphibian neurulae. Maximum band separation and resolution was achieved by using a dissociating discontinuous buffer with gels made of a discontinuous gradient of acrylamide. 相似文献
23.
Ya‐Ching Shen Yun‐Sheng Lin Shaw‐Man Hsu Ashraf Taha Khalil Shih‐Sheng Wang Ching‐Te Chien Yao‐Haur Kuo Chang‐Hung Chou 《Helvetica chimica acta》2007,90(7):1319-1329
The phytochemical investigation of the more polar fractions from the leaves and twigs of Taxus sumatrana (Taxaceae) afforded five new taxane diterpene esters, tasumatrols P–T ( 1 – 5 ) possessing an 11(15→1),11(10→9)‐diabeotaxane skeleton. Compounds 1, 4 , and 5 contain an α‐hydroxy group at C(14), while 3 has no OH group at either C(13) or C(14). Compound 2 is a natural 4,5‐acetonide derivative, while 4 has an unusual spiro‐connected 2‐hydroxy‐2‐phenyl‐1,3‐dioxolane ring. Ten known taxoids, were also isolated in the course of the chromatographic fractionation. Five additional new O‐acetyl derivatives 3a, 4a, 4b, 5a , and 5b were prepared from the taxanes 3 – 5 . The structures of all new compounds were established on the basis of their spectroscopic analyses. Compound 1 showed mild cytotoxic activity against human Hela and Daoy tumor cells. 相似文献
24.
25.
A response equation for conductivity detection in ion chromatography has been derived. This equation is applicable to non-suppressed ion chromatography using both fully ionised and partially ionised eluents. A prime assumption of this equation is that when partially ionised eluents are used (such as benzoic acid), both the ionised and neutral components of the eluent species contribute to the detector response of anionic analytes. Experimental evidence is provided to support this assumption in that pH changes accompanying the elution of an analyte have been measured. These pH changes are proportional to the concentration of analyte injected onto the column, in accordance with predictions from the response equation. Furthermore, it is shown that protonated eluents (such as benzoic acid) give more sensitive detection than equivalent ionised eluents (such as potassium benzoate) and the signal enhancement achieved using a protonated eluent species is in accordance with theory. 相似文献
26.
The mass spectra of isohumulones (IV, V), tetrahydroisocohumulones (VI, VII), tetrahydroisohumulones (VIII) neohydroisocohumulones (XI, XII) cohumulinic acid (III), lupuloxinic acid (XV), humulinone (XIV) and related compounds are described. Ions which appear to be diagnostic for particular structures are discussed. 相似文献
27.
28.
A D C, spectrochemical method using the STALLWOOD jet has been developed for the determination of Li, Na, K and Rb in silicate minerals and rocks. Samples are mixed with graphite and Cs2CO3 in tho ratio 2 : 1 : 1, and Cs serves as internal standard. Precision and accuracy is satisfactory. 相似文献
29.
A review is presented detailing the development and use of suppression devices for the conductimetric detection of inorganic ions by ion chromatography (IC). An overview of the general response equation for conductivity detection is also given. Topics of discussion include the role and function of suppressors, the development of early suppressors including packed column and membrane devices from 1975 to 1990 and the subsequent progression towards present day commercially available suppressors and recent innovations. Post-suppression devices for signal enhancement are also discussed. 相似文献
30.
Andrzej Maączyński Marian Góral Barbara Wiśniewska-Gocłowska Adam Skrzecz David Shaw 《Monatshefte für Chemie / Chemical Monthly》2003,134(5):633-653
Summary. The evaluation of mutual solubility data for systems water with n-alkanes, isoalkanes, and cycloalkanes along the three phase line is reported and a formula for the prediction of solubility
of alkanes in water is developed. Then a cubic equation of state with an added term, which accounts for hydrogen bonding is
used for correlation of liquid–liquid equilibrium data and for prediction of solubility of water in hydrocarbons using alkane
in water solubility data. Comparison of the predicted and experimental solubilities is performed using all accessible experimental
data. With this approach it is possible to predict the solubilities of water in alkanes with good accuracy over the temperature
range up to about 20 K below critical temperature. Solubility of alkanes in water can also be calculated using experimental
data for solubility of water in alkanes but results of these calculations are more sensitive to experimental errors of the
data.
Corresponding author: E-mail: macz@ichf.edu.pl
Received August 5, 2002; accepted (revised) September 13, 2002
Published online March 13, 2003
RID="a"
ID="a" Dedicated to Prof. Dr. H. Gamsj?ger on the occasion of his 70th birthday anniversary 相似文献