全文获取类型
收费全文 | 6222篇 |
免费 | 368篇 |
国内免费 | 46篇 |
专业分类
化学 | 4277篇 |
晶体学 | 69篇 |
力学 | 265篇 |
数学 | 938篇 |
物理学 | 1087篇 |
出版年
2023年 | 48篇 |
2022年 | 78篇 |
2021年 | 212篇 |
2020年 | 150篇 |
2019年 | 262篇 |
2018年 | 222篇 |
2017年 | 161篇 |
2016年 | 327篇 |
2015年 | 206篇 |
2014年 | 329篇 |
2013年 | 626篇 |
2012年 | 390篇 |
2011年 | 395篇 |
2010年 | 279篇 |
2009年 | 270篇 |
2008年 | 286篇 |
2007年 | 258篇 |
2006年 | 248篇 |
2005年 | 202篇 |
2004年 | 178篇 |
2003年 | 155篇 |
2002年 | 197篇 |
2001年 | 82篇 |
2000年 | 123篇 |
1999年 | 70篇 |
1998年 | 57篇 |
1997年 | 58篇 |
1996年 | 43篇 |
1995年 | 41篇 |
1994年 | 48篇 |
1993年 | 44篇 |
1992年 | 37篇 |
1991年 | 27篇 |
1990年 | 24篇 |
1989年 | 40篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1986年 | 22篇 |
1985年 | 39篇 |
1984年 | 35篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 28篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 20篇 |
1977年 | 12篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1973年 | 10篇 |
排序方式: 共有6636条查询结果,搜索用时 296 毫秒
951.
952.
Shariq Ali Norah Albekairi Xiao-Ming Wang Svetlana Patrikeeva Tatiana N. Nanovskaya Mahmoud S. Ahmed 《液相色谱法及相关技术杂志》2018,41(5):232-238
Ex vivo placental perfusion experiments are important in understanding the quantity and mechanisms of xenobiotic transport to the fetus during pregnancy. Our study demonstrates that paclitaxel and antipyrine concentrations in placental perfusion medium containing physiological concentrations of human serum albumin during pregnancy (30?mg/mL) can be quantified by RP-HPLC and UV detection. A liquid-liquid extraction method was developed for the quantification of paclitaxel and celecoxib (internal standard) from perfusion medium. Antipyrine, which is a necessary marker in placental perfusions for determining the validity of experiments and calculating the clearance index of xenobiotics, was also analyzed by HPLC and UV detection. Antipyrine concentrations were determined by HPLC after precipitating the perfusion medium in acetonitrile and separating the precipitated proteins by centrifugation. Concentrations were fitted to linear regressions with R2 values approaching 1. Lower limits of detection for paclitaxel and antipyrine were 100?ng/mL and 200?ng/mL, respectively. Both methods demonstrated high intra-day and inter-day precision and trueness. Additionally, the use of these methods was demonstrated in a placental perfusion experiment using Taxol® (paclitaxel dissolved in Cremophor-EL). The fetal transfer rate of Taxol was 6.6% after 1 hour. 相似文献
953.
Mahdi Ghorbani Mahmoud Chamsaz Gholam Hossein Rounaghi 《Analytical and bioanalytical chemistry》2016,408(16):4247-4256
954.
Elías-Zúñiga Alex Palacios-Pineda Luis Manuel Olvera-Trejo Daniel Martínez-Romero Oscar 《Nonlinear dynamics》2020,102(3):1239-1270
Nonlinear Dynamics - In this paper, the dynamics response of a finite extensibility nonlinear elastic (FENE) absorber attached to a nonlinear primary system is investigated by writing the modal... 相似文献
955.
956.
Dr. Jan Nekvinda Michael Kugler Dr. Josef Holub Dr. Suzan El Anwar Dr. Jiří Brynda Klára Pospíšilová Dr. Zdeňka Růžičková Dr. Pavlína Řezáčová Dr. Bohumír Grüner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16541-16553
Carbonic anhydrase IX (CA IX), a tumor-associated metalloenzyme, represents a validated target for cancer therapy and diagnostics. Herein, we report the inhibition properties of isomeric families of sulfonamidopropyl-dicarba-closo-dodecaboranes group(s) prepared using a new direct five-step synthesis from the corresponding parent cages. The protocol offers a reliable solution for synthesis of singly and doubly substituted dicarba-closo-dodecaboranes with a different geometric position of carbon atoms. The closo-compounds from the ortho- and meta-series were then degraded to corresponding 11-vertex dicarba-nido-undecaborate(1−) anions. All compounds show in vitro enzymatic activity against CA IX in the low nanomolar or subnanomolar range. This is accompanied by clear isomer dependence of the inhibition constant (Ki) and selectivity towards CA IX. Decreasing trends in Ki and selectivity index (SI) values are observed with increasing separation of the cage carbon atoms. Interactions of compounds with the active sites of CA IX were explored with X-ray crystallography, and eight high-resolution crystal structures uncovered the structural basis of inhibition potency and selectivity. 相似文献
957.
Counterfeiting of pharmaceuticals has become a serious problem all over the world, particularly in developing countries. In the present work, a highly sensitive LC–MS/MS method was developed for simultaneous determination of tramadol hydrochloride in the presence of some suspected mislabeled drugs such as alprazolam, diazepam, chlorpheniramine maleate, diphenylhydramine and paracetamol. The prepared samples were analyzed on an API 4000 mass spectrometer using an Eclipse C18 column (3.5 μm, 4.6 × 100 mm). The mobile phase consisting of 0.01% formic acid, acetonitrile and methanol (60:20:20 v/v/v) was pumped with an isocratic elution at a flow rate of 0.7 mL min?1. The detection was achieved on a triple quadruple tandem mass spectrometer in multiple reaction monitoring mode. The proposed method was successfully validated according to International Conference on Harmonization guidelines with respect to accuracy, precision, linearity, limit of detection and limit of quantitation. The calibration linear range for tramadol hydrochloride, alprazolam, diazepam, chlorpheniramine maleate, diphenylhydramine and paracetamol was 5–500 ng mL?1. The results revealed that the applied method is promising for the differentiation of genuine tramadol tablets from counterfeit ones without prior separation. 相似文献
958.
In this work, low‐moisture glycidyl azide polymer (GAP) was successfully prepared using a modified two‐step method. The modified method resembles the structure of the classical two‐step method, which is widely used to prepare the GAP. Firstly, epichlorohydrin (ECH) is polymerized into polyepicholorohydrin (PECH), which is subjected afterward to azidation step using sodium azide (NaN3). Interestingly, minimizing the water content in the final GAP product, which is a challenging when dealing with GAP as a rocket propellant binder, was effectively achieved by utilizing low boiling point solvents instead of the relatively high boiling point Dimethyl formamide (DMF), monitoring the volatility of ECH and controlling the exothermicity of the reaction. Prepared GAP samples were investigated using Fourier transformer infra‐red (FT‐IR), gel‐permeation chromatography (GPC) and elemental analysis apparatus (CHNS) were used to characterize the product. The moisture % in the final product was examined using the Karl‐Fisher Technique. Results showed the successful preparation of GAP with low water content (<0.01 %), high average molecular weight (> 2000 g · mol–1), 42.82 % nitrogen, a viscosity of 3484 cP at 20 °C, yield ranges between 95–98 % and a polydispersity index of 1.2. The prepared GAP is promising for replacement of the classical GAPs in the energetic materials applications. 相似文献
959.
Lgaz Hassane Chaouiki Abdelkarim Albayati Mustafa R. Salghi Rachid El Aoufir Yasmina Ali Ismat H. Khan Mohammad I. Mohamed Shaaban K. Chung Ill-Min 《Research on Chemical Intermediates》2019,45(4):2269-2286
Research on Chemical Intermediates - Mild steel corrosion in HCl solution is an example of corrosion in acidic mediums. The ongoing research efforts to develop novel environmentally friendly... 相似文献
960.
Jan Sklyaruk Jannik C. Borghs Osama El‐Sepelgy Magnus Rueping 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(3):785-789
A metal‐catalyzed methylation process has been developed. By employing an air‐ and moisture‐stable manganese catalyst together with isotopically labeled methanol, a series of D‐, CD3‐, and 13C‐labeled products were obtained in good yields under mild reaction conditions with water as the only byproduct. 相似文献