全文获取类型
收费全文 | 3962篇 |
免费 | 141篇 |
国内免费 | 31篇 |
专业分类
化学 | 2825篇 |
晶体学 | 17篇 |
力学 | 140篇 |
数学 | 593篇 |
物理学 | 559篇 |
出版年
2024年 | 6篇 |
2023年 | 35篇 |
2022年 | 92篇 |
2021年 | 91篇 |
2020年 | 90篇 |
2019年 | 87篇 |
2018年 | 58篇 |
2017年 | 45篇 |
2016年 | 134篇 |
2015年 | 101篇 |
2014年 | 138篇 |
2013年 | 236篇 |
2012年 | 277篇 |
2011年 | 312篇 |
2010年 | 188篇 |
2009年 | 187篇 |
2008年 | 288篇 |
2007年 | 267篇 |
2006年 | 204篇 |
2005年 | 230篇 |
2004年 | 197篇 |
2003年 | 138篇 |
2002年 | 146篇 |
2001年 | 45篇 |
2000年 | 37篇 |
1999年 | 29篇 |
1998年 | 31篇 |
1997年 | 34篇 |
1996年 | 41篇 |
1995年 | 38篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 23篇 |
1991年 | 23篇 |
1990年 | 31篇 |
1989年 | 16篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有4134条查询结果,搜索用时 15 毫秒
91.
In this paper we report a simple methodology for obtaining (+) trans - 1,2 - epoxylimonene (1b) in high purity (>99% HRGC) and reasonable quantity. The mixture of 1a and 1b in CH2Cl2 is stirred with 1M NaHSO3 in water. Under these conditions 1a is completely destroyed, while 1b is only partially destroyed. 相似文献
92.
Numerical differencing schemes are subject to dispersive and dissipative errors, which in one dimension, are functions of a wavenumber. When these schemes are applied in two or three dimensions, the errors become functions of both wavenumber and the direction of the wave. For the Euler equations, the direction of flow and flow velocity are also important. Spectral analysis was used to predict the error in magnitude and direction of the group velocity of vorticity–entropy and acoustic waves in the solution of the linearised Euler equations in a two‐dimensional Cartesian space. The anisotropy in these errors, for three schemes, were studied as a function of the wavenumber, wave direction, mean flow direction and mean flow Mach number. Numerical experiments were run to provide confirmation of the developed theory. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
93.
Dr. Manuel Moliner Prof. Fernando Rey Prof. Avelino Corma 《Angewandte Chemie (International ed. in English)》2013,52(52):13880-13889
Zeolites are crystalline microporous materials with application in diverse fields, especially in catalysis. The ability to prepare zeolites with targeted physicochemical properties for a specific catalytic application is a matter of great interest, because it allows the efficiency of the entire chemical process to be increased (higher product yields, lower undesired by‐products, less energy consumption, and cost savings, etc). Nevertheless, directing the zeolite crystallization towards the material with the desired framework topology, crystal size, or chemical composition is not an easy task, since several variables influence the nucleation and crystallization processes. The combination of accumulated knowledge, rationalization, and innovation has allowed the synthesis of unique zeolitic structures in the last few years. This is especially true in terms of the design of organic and inorganic structure‐directing agents (SDAs). In this Minireview we will present the rationale we have followed in our studies to synthesize new zeolite structures, while putting this in perspective with the advances made by other researchers of the zeolite community. 相似文献
94.
95.
Karl Pays Caroline Mabille Véronique Schmitt Fernando Leal-Calderon J´erôme Bibette 《Journal of Dispersion Science and Technology》2013,34(1-3):175-186
This paper aims to review the various degradation pathays of emulsions. Aging of emulsions may proceed through three distinct microscopic mechanisms: diffusion or permeation, dewetting, and coalescence, each one being associated with a very characteristic growth scenario. We show within this context how double emulsions are a unique tool to complete the basic understanding of emulsion metastability. 相似文献
96.
Dr. Ruth Matesanz Dr. José Fernando Diaz Dr. Francisco Corzana Andrés G. Santana Dr. Agatha Bastida Dr. Juan Luis Asensio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(10):2875-2889
The most common mode of bacterial resistance to aminoglycoside antibiotics is the enzyme‐catalysed chemical modification of the drug. Over the last two decades, significant efforts in medicinal chemistry have been focused on the design of non‐ inactivable antibiotics. Unfortunately, this strategy has met with limited success on account of the remarkably wide substrate specificity of aminoglycoside‐modifying enzymes. To understand the mechanisms behind substrate promiscuity, we have performed a comprehensive experimental and theoretical analysis of the molecular‐recognition processes that lead to antibiotic inactivation by Staphylococcus aureus nucleotidyltransferase 4′(ANT(4′)), a clinically relevant protein. According to our results, the ability of this enzyme to inactivate structurally diverse polycationic molecules relies on three specific features of the catalytic region. First, the dominant role of electrostatics in aminoglycoside recognition, in combination with the significant extension of the enzyme anionic regions, confers to the protein/antibiotic complex a highly dynamic character. The motion deduced for the bound antibiotic seem to be essential for the enzyme action and probably provide a mechanism to explore alternative drug inactivation modes. Second, the nucleotide recognition is exclusively mediated by the inorganic fragment. In fact, even inorganic triphosphate can be employed as a substrate. Third, ANT(4′) seems to be equipped with a duplicated basic catalyst that is able to promote drug inactivation through different reactive geometries. This particular combination of features explains the enzyme versatility and renders the design of non‐inactivable derivatives a challenging task. 相似文献
97.
98.
99.
Shuichi Hirata Kouichi Tanaka Katsuya Matsui Fernando Arteaga Arteaga Yasushi Yoshida Shinobu Takizawa Hiroaki Sasai 《Tetrahedron: Asymmetry》2013,24(19):1189-1192
The introduction of a 1,3-propanediamine unit at the 3-position of (S)-BINOL using a methylene spacer led to the formation of a chiral bifunctional organocatalyst for the aza-Morita–Baylis–Hillman (aza-MBH) reaction. The organocatalyst 1k mediated aza-MBH transformations with high chemical yields and with up to 82% ee. 相似文献