全文获取类型
收费全文 | 97966篇 |
免费 | 18468篇 |
国内免费 | 21413篇 |
专业分类
化学 | 38012篇 |
晶体学 | 2559篇 |
力学 | 4468篇 |
综合类 | 2164篇 |
数学 | 9132篇 |
物理学 | 27500篇 |
无线电 | 54012篇 |
出版年
2024年 | 546篇 |
2023年 | 1531篇 |
2022年 | 3665篇 |
2021年 | 3469篇 |
2020年 | 3229篇 |
2019年 | 2935篇 |
2018年 | 2933篇 |
2017年 | 4187篇 |
2016年 | 3154篇 |
2015年 | 4780篇 |
2014年 | 5941篇 |
2013年 | 7333篇 |
2012年 | 8042篇 |
2011年 | 8386篇 |
2010年 | 8369篇 |
2009年 | 8567篇 |
2008年 | 9114篇 |
2007年 | 8832篇 |
2006年 | 8305篇 |
2005年 | 6936篇 |
2004年 | 5313篇 |
2003年 | 3710篇 |
2002年 | 3337篇 |
2001年 | 3430篇 |
2000年 | 3377篇 |
1999年 | 1727篇 |
1998年 | 791篇 |
1997年 | 591篇 |
1996年 | 580篇 |
1995年 | 520篇 |
1994年 | 523篇 |
1993年 | 531篇 |
1992年 | 490篇 |
1991年 | 321篇 |
1990年 | 296篇 |
1989年 | 315篇 |
1988年 | 291篇 |
1987年 | 235篇 |
1986年 | 216篇 |
1985年 | 147篇 |
1984年 | 152篇 |
1983年 | 133篇 |
1982年 | 105篇 |
1981年 | 86篇 |
1980年 | 77篇 |
1979年 | 89篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1965年 | 35篇 |
1959年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Studies on the Interaction of Beryllon Ш with Proteins by Voltammetric Technique and its Application 总被引:1,自引:0,他引:1
A new quantitative determination method of proteins using beryllon Ш by voltammetric technique was developed in this paper. In pH 3.5 Britton-Robinson (B-R) buffer solution, beryllon Ш can bind with human serum albumin (HSA) to form an electro-inactive supermolecular complex. Beryllon Ш has a well-defined voltammetric reduction peak at -0.38 V (vs. SCE) and the addition of protein in this solution can cause the decrease of the reductive peak current. Based on the decrease of the reduction peak current, a new electrochemical method for the determination of HSA was established with linear range of 1.0~40.0 mg/L and the detection limit of 1.0 mg/L. This method is further applied to the determination of real sample of healthy human serum. 相似文献
942.
943.
A cDNA for human TNF-α (615bp) was isolated by means of polymerase chain reaction (PCR) using first strand cDNA from PMA-induced HL-60 cells as template. The result from sequencing the 615 bp cDNA fragment indicated that it corresponded to the entire sequence of mature human TNF coding region. Direct expression of mature human TNF was achieved using a plasmid pHT-1 constructed by ligation of the cDNA and a synthetic DNA. The IPTG-induced bacterial product (hTNF) showed cytotoxicity to mouse L-929 cells. The TNF activity was further identified by neutralization of a specific monoclonal antibody against human TNF-α. Approximately 80,000 units of activity were detected per ml of culture at A600=2. 相似文献
944.
Determination of Partial Molar Volumes of EPA and DHA Ethyl Esters in Supercritical Carbon Dioxide 总被引:4,自引:0,他引:4
Mei HUANG Xian Da WANG Ren Tian XIONG Ping Dong WU Qi Long REN* National Laboratory of Secondary Resources Chemical Engineering Zhejiang University Hangzhou 《中国化学快报》2002,13(1)
The use of supercritical fluids (SCFs) as solvents has been attracting widespread interest in the research and commercial applications. The study of partial molar volumes of solutes at infinite dilution in the near-critical region is of considerable fundamental importance, as these data reflects the interactions occurring between the solute and the solvent. Experimental measurements of partial molar volumes may be divided into two categories: direct and indirect methods. The direct methods… 相似文献
945.
946.
947.
New binuclear copper(Ⅱ) complexes, [Cu(samen)Cu(NO_2-phen)]·H_2O and [Cu(sampn)-Cu(NO_2-phen)]·2H_2O have been synthesized, where samen~(4-), sampn~(4-) and NO_2-phen denote N, N′-ethylenedisalicylamidate anion, N, N′-1, 2-propanedisalicylamidate anion and 5-nitro-1, 10-phenanthroline respectively. 3ased on IR, elemental analyses and electronic spectra, the complexes are proposed to have a phenoxy-bridged structure and to consist of the Cu(Ⅱ)ion in distorted planar environment. The complexes have been characterized with varlable-temperature magnetic susceptibility (4—300 K) and the observed data were fit to those from a modified Bleaney-Bowers equation by least-squares method, giving the exchange integral J=-63.0 cm~(-1) (samen) and J=-46.5cm~(-1) (sampn). This indicates the existence of antiferromagnetic spin exchange interaction among the metal ions. 相似文献
948.
StudiesonColloidalPropertiesofMixedMetalHydroxide-ClayAqueousSuspensionNOUwan-guo;ZHANGChun-guang;SUNDe-jun;HANShu-huaandWANG... 相似文献
949.
2-取代亚肼基-1,3-二硫杂环戊烷类化合物的合成及其生物活性研究 总被引:9,自引:0,他引:9
以取代苯甲醛、取代吡啶和取代苯甲酸酯等为原料合成了 10种含硫杂环化合物 (其中 2a~ 2g化合物为国内外未见报道 ) .在合成过程中采用了超声波技术 ,极大地缩短了反应时间 ,提高了收率 .所得化合物的结构经IR ,1 HNMR ,MS和元素分析证实 .对其生物活性进行了初步测试 ,结果证明一些化合物具有良好的抑菌或杀菌作用 ,其中 2b ,2c ,2e ,2h ,2i和2j对大肠杆菌 ( 10 40 7号 )的抗菌效果与CET和SMZ相当 ;2b ,2c ,2f对草绿色链球菌 ( 112 3号 )的抗菌效果与CET和SMZ相当 . 相似文献
950.
Introduction Diastereoselective construction of 1,3-diheteroatom units, especially 1,3-amino alcohols and 1,3-diols, has always been in high demands in synthetic organic chemistry, as they are widely present in many natural products and potent drugs, such as nucleoside antibiot-ics and the HIV protease inhibitors.1,2 They have also been used as chiral ligands for asymmetric catalysts and as synthetic intermediates.3 Although several methods for the construction of 1,3-amino alcohols have been… 相似文献