全文获取类型
收费全文 | 22270篇 |
免费 | 3902篇 |
国内免费 | 3501篇 |
专业分类
化学 | 16881篇 |
晶体学 | 491篇 |
力学 | 1175篇 |
综合类 | 309篇 |
数学 | 2312篇 |
物理学 | 8505篇 |
出版年
2024年 | 52篇 |
2023年 | 326篇 |
2022年 | 579篇 |
2021年 | 707篇 |
2020年 | 783篇 |
2019年 | 920篇 |
2018年 | 727篇 |
2017年 | 728篇 |
2016年 | 996篇 |
2015年 | 1090篇 |
2014年 | 1237篇 |
2013年 | 1646篇 |
2012年 | 2084篇 |
2011年 | 2036篇 |
2010年 | 1605篇 |
2009年 | 1591篇 |
2008年 | 1766篇 |
2007年 | 1480篇 |
2006年 | 1505篇 |
2005年 | 1354篇 |
2004年 | 1106篇 |
2003年 | 867篇 |
2002年 | 950篇 |
2001年 | 737篇 |
2000年 | 583篇 |
1999年 | 467篇 |
1998年 | 285篇 |
1997年 | 214篇 |
1996年 | 197篇 |
1995年 | 168篇 |
1994年 | 174篇 |
1993年 | 142篇 |
1992年 | 81篇 |
1991年 | 104篇 |
1990年 | 61篇 |
1989年 | 47篇 |
1988年 | 46篇 |
1987年 | 22篇 |
1986年 | 35篇 |
1985年 | 38篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1957年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
71.
72.
Yuhua Xue Jun Liu Hao Chen Ruigang Wang Dingqiang Li Jia Qu Liming Dai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(48):12300-12300
73.
74.
75.
Non-linear modeling and dynamic analysis of hydraulic control valve; effect of a decision factor between experiment and numerical simulation 总被引:1,自引:0,他引:1
Numerical problems that are usually ignored in the dynamic analysis of hydraulic control valves are described, and an analysis of the effects of such problems on the numerical modeling is provided. Previous studies have ignored the effects of changes in the flow coefficient in the orifice, the solenoid force along the spool movement in the valve and an ascending tendency of pressure during reach to the steady state. To eliminate these problems, it was studied a method to substantiate the non-linearity of the pressure loss caused by passing between the orifice and port as well as that caused by interaction with the solenoid. Moreover, the movement of the spool and spring is expressed using the time-delay-element (TDE). The proposed numerical model has been used in the Bond graphs method of a hydraulic control valve and the simulation results have been shown to be accurate. It is known that differences between simulated and experimental results can have a considerable impact on the function of actual systems. The contribution of each parameter is measured separately for the transient state and steady state. Analysis standard observed the first peak value, pressure increase to the steady state and the settling time in the response results. 相似文献
76.
Xiao-Yi Song Yu-Hang Zhang Ping-Ping Sun Prof. Dr. Jun Gao Prof. Dr. Fa-Nian Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(25):5654-5661
Novel lithium–lanthanide (Ln: cerium and praseodymium) bimetallic coordination polymers with formulas C10H2LnLiO8 (Ln: Ce (CeLipma) and Pr (PrLipma)) and C10H3CeO8 (Cepma) were prepared through a simple hydrothermal method. The three compounds were characterized by means of FTIR spectroscopy, X-ray diffraction, single-crystal X-ray diffraction, SEM, TEM, and X-ray photoelectron spectroscopy. The results of structural refinement show that they belong to triclinic symmetry and P space group with cerium (or praseodymium) and lithium cations, forming coordination bonds to oxygen atoms from different pyromellitic acid molecules, and leading to the construction of 3D structures. It is interesting to note that the frameworks exclude any coordination water and lattice water. As an electrode material for lithium-ion batteries, CeLipma exhibits a maximum capacity of 800.5 mAh g−1 and a retention of 91.4 % after 50 cycles at a current density of 100 mA g−1. The favorable electrochemical properties of the lanthanide coordination polymers show potential application prospects in the field of electrode materials. 相似文献
77.
Bioactive membranes for guided tissue regeneration would be of value for periodontal therapy. Chitosan-multiwall carbon nanotube (CS-MWNT) composites were treated to deposit nanoscopic apatite for MWNT proportions of 0-4 mass%. Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction were used for characterization. Apatite was formed on the CS-MWNT composites at low MWNT concentrations, but the dispersion of the MWNT affects the crystallite size and the Ca/P molar ratio of the composite. The smallest crystallite size was 9 nm at 1 mass% MWNT. 相似文献
78.
79.
Wenxue Li Jun Wen Jingyu He Di Cao Fanlu Sun Jinying Li Guorong Fan 《Journal of separation science》2013,36(19):3184-3190
A simple, rapid, high‐throughput, and highly sensitive LC–MS/MS was developed to determine anisodamine in a small volume (50 μL) of beagle dog plasma using atropine sulfate as the internal standard. The analyte and internal standard were isolated from 50 μL plasma samples after a one‐step protein precipitation using Sirocco 96‐well protein precipitation filtration plates. The separation was accomplished on a Hanbon Hedera CN column (100 × 4.6 mm, 5 μm) and the run time was 4 min. A Micromass Quatro Ultima mass spectrometer equipped with an ESI source was operated in the multiple reaction monitoring mode with the precursor‐to‐product ion transitions m/z 306.0→140.0 (anisodamine) and 290.0→123.9 (atropine) used for quantitation. The method was sensitive with a low LOQ of 0.05 ng/mL, and good linearity in the range 0.05–50 ng/mL for anisodamine (r2 ≥ 0.995). All the validation data, such as accuracy, intra‐ and interrun precision, were within the required limits. The method was successfully applied to the pharmacokinetic study of anisodamine hydrochloride injection in beagle dogs. 相似文献
80.
In life sciences,molecules are categorized into biological macromolecules(protein,DNA,RNA etc.)and small molecules(neurotransmitters,vitamins,drugs,natural products,water etc.).The main methodology of chemistry for life sciences is using chemical techniques and tools to explore and manipulate the functions of biological macromolecules.This methodology can be traced back to W hler’s synthesis of urea from"inorganic"compounds in 1828.Today,we realize that chemistry can advance a molecular understanding of biology,and the harnessing of biology can advance chemical knowledge as well[1–4].Chemicals are widely used as probes to investigate biological functions[5–7]. 相似文献