全文获取类型
收费全文 | 1331篇 |
免费 | 20篇 |
国内免费 | 17篇 |
专业分类
化学 | 833篇 |
晶体学 | 9篇 |
力学 | 41篇 |
数学 | 189篇 |
物理学 | 296篇 |
出版年
2022年 | 11篇 |
2021年 | 15篇 |
2020年 | 14篇 |
2017年 | 10篇 |
2016年 | 20篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 67篇 |
2012年 | 35篇 |
2011年 | 66篇 |
2010年 | 45篇 |
2009年 | 31篇 |
2008年 | 43篇 |
2007年 | 63篇 |
2006年 | 48篇 |
2005年 | 53篇 |
2004年 | 48篇 |
2003年 | 38篇 |
2002年 | 44篇 |
2001年 | 32篇 |
2000年 | 36篇 |
1999年 | 35篇 |
1998年 | 12篇 |
1997年 | 20篇 |
1996年 | 32篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 32篇 |
1992年 | 12篇 |
1991年 | 20篇 |
1990年 | 26篇 |
1989年 | 19篇 |
1988年 | 17篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 28篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 14篇 |
1974年 | 10篇 |
1973年 | 11篇 |
1972年 | 12篇 |
1968年 | 9篇 |
排序方式: 共有1368条查询结果,搜索用时 31 毫秒
101.
102.
A unique geometry of the active site of angiotensin-converting enzyme consistent with structure-activity studies 总被引:1,自引:0,他引:1
Dorica Mayer Christopher B. Naylor Ioan Motoc Garland R. Marshall 《Journal of computer-aided molecular design》1987,1(1):3-16
Summary Previous structure-activity studies of captopril and related active angiotensin-converting enzyme (ACE) inhibitors have led to the conclusion that the basic structural requirements for inhibition of ACE involve (a) a terminal carboxyl group; (b) an amido carbonyl group; and (c) different types of effective zinc (Zn) ligand functional groups. Such structural requirements common to a set of compounds acting at the same receptor have been used to define a pharmacophoric pattern of atoms or groups of atoms mutually oriented in space that is necessary for ACE inhibition from a stereochemical point of view. A unique pharmacophore model (within the resolution of approximately 0.15 Å) was observed using a method for systematic search of the conformational hyperspace available to the 28 structurally different molecules under study. The method does not assume a common molecular framework, and, therefore, allows comparison of different compounds that is independent of their absolute orientation.Consequently, by placing the carboxyl binding group, the binding site for amido carbonyl, and the Zn atom site in positions determined by ideal binding geometry with the inhibitors' functional groups, it was possible to clearly specify a geometry for the active site of ACE. 相似文献
103.
104.
María U. Alzueta Marta Guerrero Ángela Millera Paul Marshall Peter Glarborg 《Proceedings of the Combustion Institute》2021,38(1):575-583
Oxidation of acetonitrile has been studied in a flow reactor in the absence and presence of nitric oxide. The experiments were conducted at atmospheric pressure in the temperature range 1150–1450 K, varying the excess air ratio from slightly fuel-lean to very lean. Oxidation of CH3CN was slow below 1300 K. Nitric oxide, hydrogen cyanide and nitrous oxide were detected as important products. A detailed chemical kinetic model for oxidation of acetonitrile was developed, based on a critical evaluation of data from literature. The rate coefficients for the reactions of CH3CN and CH2CN with O2 were calculated from ab initio theory. Modeling predictions were in satisfactory agreement with experiments. Calculations were sensitive to thermal dissociation of CH3CN and to the branching fraction for CH3CN + OH to CH2CN + H2O and HOCN + CH3, respectively. More work is desirable for these steps, as well as for reactions of CH2CN and HCCN. 相似文献
105.
Marshall Slemrod Athanasios E. Tzavaras 《Archive for Rational Mechanics and Analysis》1993,122(4):353-392
This report discusses a new approach for the resolution of the fluid-dynamic limit for the Broadwell system of the kinetic theory of gases, appropriate in the case of Riemann, Maxwellian data. Since the formal limiting system is expected to have self-similar solutions, we are motivated to replace the Knudsen number in the Broadwell model so that the resulting model admits self-similar solutions =x/t and then let go to zero. The limiting procedure is justified and the resulting limit is a solution of the Riemann problem for the fluid-dynamic limit equations. A class of Riemann data for which this program can be carried out is exhibited. Furthermore, it is shown that for the Carleman model the complete program can be done successfully for arbitrary Riemann data. 相似文献
106.
Mikhail?Feldman Seung-Yeal?Ha Marshall?SlemrodEmail author 《Archive for Rational Mechanics and Analysis》2005,178(1):81-123
In this paper, we present a new geometric level-set formulation of a plasma-sheath interface arising in plasma physics. We formally derive the explicit dynamics of the interface from the Euler-Poisson equations and study the local-time evolution of the interface and sheath in some special cases. 相似文献
107.
Gregory T. Bourne Dr. Daniel J. Kuster Dr. Garland R. Marshall Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(28):8439-8445
Phenylpyridal‐ and phenyldipyridal‐based scaffolds have been designed and synthesized as novel helical peptide mimetics. The synthesis required optimisation and selective alkylation in producing 2,6‐functionalized 3‐hydroxypyridine derivatives for a convergent scheme. The pyridine analogues were coupled by a series of Suzuki/Stille types cross‐coupling reactions. A series of biaryl and ter‐aryl substituted heterocycles were produced. The synthetic approach was concise and high yielding allowing large variability at the wanted side‐chain attachment points. A number of compounds were synthesised to show the versatility of the strategy. 相似文献
108.
The preparation of bis-protected phloroglucinol derivatives from a range of protected resorcinol substrates is presented. Functionalization was achieved via a two-step, one-pot iridium-catalyzed C-H activation/borylation/oxidation protocol. Our system gave high conversions to the arylboronic esters and good yields of the desired phenols following subsequent oxidation. A range of common protecting group categories was studied including alkyl, silyl, ether and ester. 相似文献
109.
Electrochemical reactions in the electrochemical treatment of tumors (EChT) induce extreme pH changes and, consequently, protein electrodenaturation fronts intimately related to tumor destruction. Here we introduce a new in vitro EChT collagen–macronutrient gel (CMG) model to study protein electrodenaturation fronts as a mean of assessing EChT effectiveness. Our CMG model shows that from an initial uniform condition two electrodenaturation fronts evolve expanding towards each other until collision. Moreover, electrodenaturation front tracking reveals that the front grows under a diffusion-controlled regime. Based on this evidence it is possible, in principle, to predict the time needed for tumor destruction without compromising healthy tissue. These results are consistent with those previously obtained with in vivo and in vitro EChT modeling. In contrast to previous simpler in vitro models, our CMG model represents a better structural and chemical approximation to a real tissue thus providing a better tool for validation of new in silico EChT models aimed at a more accurate prediction of tissue destruction level. 相似文献
110.
Declan Williams Suzanne Ackloo Peihong Zhu Peter Bowden Kenneth R. Evans Christina L. Addison Chris Lock John G. Marshall 《Analytical and bioanalytical chemistry》2010,396(3):1223-1247
The endogenous peptides of human serum may have regulatory functions, have been associated with physiological states, and
their modifications may reveal some mechanisms of disease. In order to correlate levels of specific peptides with disease
alongside internal standards, the polypeptides must first be reliably extracted and identified. Endogenous blood peptides
can be effectively enriched by precipitation of the serum with organic solvents followed by selective extraction of peptides
using aqueous solutions modified with organic solvents. Polypeptides on filter paper were assayed with Coomasie brilliant
blue binding. The polypeptides were resolved by detergent tricine polyacrylamide electrophoresis and visualized by diamine
silver staining. Peptides in the extracts were collected by C18 and analyzed by matrix-assisted laser desorption/ionization
and liquid chromatography–electrospray ionization–tandem mass spectrometry (MS/MS) quadrupole time-of-flight MS/MS. Peptides
were resolved as multiple isotopic peaks in MS mode with mass deviation of 0.1 Da or less and similar accuracy for fragments.
The sensitivity of MS and MS/MS analysis was estimated to be in the picomolar range or less. The peptide composition of the
extracts was dependent on solvent formulation. Multiple peptides from apolipoproteins, complement proteins, coagulation factors,
and many others were identified by X!Tandem with high mass accuracy of peptide ions and fragments from collision-induced dissociation.
Many previously unreported posttranslational modifications of peptides including phosphorylations, oxidations, glycosylations,
and others were detected with high mass accuracy and may be of clinical importance. About 4,630 redundant peptides were identified
with 99% confidence separately, and together some 1,251 distinct proteins were identified with 99% confidence or greater using
the Paragon algorithm. 相似文献