全文获取类型
收费全文 | 26148篇 |
免费 | 3076篇 |
国内免费 | 4111篇 |
专业分类
化学 | 19124篇 |
晶体学 | 325篇 |
力学 | 1247篇 |
综合类 | 457篇 |
数学 | 3329篇 |
物理学 | 8853篇 |
出版年
2024年 | 18篇 |
2023年 | 222篇 |
2022年 | 410篇 |
2021年 | 560篇 |
2020年 | 616篇 |
2019年 | 661篇 |
2018年 | 551篇 |
2017年 | 504篇 |
2016年 | 855篇 |
2015年 | 935篇 |
2014年 | 1096篇 |
2013年 | 1608篇 |
2012年 | 1849篇 |
2011年 | 2772篇 |
2010年 | 1843篇 |
2009年 | 1855篇 |
2008年 | 1646篇 |
2007年 | 1558篇 |
2006年 | 1472篇 |
2005年 | 1381篇 |
2004年 | 1917篇 |
2003年 | 1433篇 |
2002年 | 1410篇 |
2001年 | 1099篇 |
2000年 | 723篇 |
1999年 | 600篇 |
1998年 | 453篇 |
1997年 | 406篇 |
1996年 | 364篇 |
1995年 | 277篇 |
1994年 | 261篇 |
1993年 | 393篇 |
1992年 | 345篇 |
1991年 | 230篇 |
1990年 | 223篇 |
1989年 | 203篇 |
1988年 | 147篇 |
1987年 | 77篇 |
1986年 | 110篇 |
1985年 | 51篇 |
1984年 | 59篇 |
1983年 | 27篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
利用X-射线衍射,扫描电镜,拉曼光谱,等离子发射光谱和比表面测定等方法研究了不同状态下失活及新鲜催化剂的结构,杂种类及含量。结果表明,超温使催化剂晶化明显,制备方法对催化剂结构有直接影响,再生使其强度降低,条形催化剂比较容易粉化,无机杂质是次要的失活原因。 相似文献
992.
XinBinMA ShengPingWANG HongLiGUO GenHuiXU 《中国化学快报》2003,14(5):461-464
Diphenyl oxalate was synthesized from transesterification of dimethyl oxalate with phenol over TS-1(2.5 wt% Ti)catalyst.TS-1 catalyst,as a beterogeneous catalyst,showed excellent selectivity of diphenyl oxalate and methylphenyl oxalate compared with other homogeneous catalysts.Lewis acid sites on TS-1 catalyst were the active sites for transesterification of dimethyl oxalate with phenol.the high selectivity was closely related to the weak acid sites over TS-1. 相似文献
993.
Pinhasov A Mei J Amaratunga D Amato FA Lu H Kauffman J Xin H Brenneman DE Johnson DL Andrade-Gordon P Ilyin SE 《Combinatorial chemistry & high throughput screening》2004,7(2):133-140
To meet growing needs for high throughput gene expression profiling, we established a new automated high throughput TaqMan RT-PCR method for quantitative mRNA expression analysis. In this method, the Allegro( trade mark ) (Zymark) system conducts all sample tracking and liquid handling steps, and ABI PRISM 7900 HT (Applied Biosystems) is used to conduct real-time determination of the C(t) value when amplification of PCR products is first detected and accumulation of inhibitory PCR products is unlikely to occur. The ABI PRISM 7900 HT Sequence Detection System features a real-time PCR instrument with 384-well-plate compatibility and robotic loading, and continuous wavelength detection, which enables the use of multiple fluorophores in a single reaction. The Allegro System offers an assembly line approach with a modular design that allows reconfiguration of the components to accommodate variations in the assay flow. In the present study, we have established and validated a new automated High Throughput (HT) TaqMan RT-PCR- based method for quantitative mRNA expression analysis. The data demonstrate that HT-Taqman PCR is a powerful tool that can be used for measuring low concentrations of mRNA, and is highly accurate, reproducible, and amenable to high throughput analysis. Results suggest that HT-TaqMan is a reliable method for the quantification of low-expression genes and a powerful tool with HT capability for target identification/validation, structure-activity relationship (SAR) study, compound selection for efficacy studies, and biomarker identification in drug discovery and development. 相似文献
994.
葡聚糖为载体的双亲型LDL吸附剂吸附动力学研究 总被引:3,自引:0,他引:3
合成了以葡聚为载体,同时具有亲水性磺酸基和疏水性胆固醇两类配基的新型低密度脂蛋白(LDL)吸附剂。通过对LDL纯溶液中吸附等温线的测试,比较了以Dextran G-75为载体的双亲型LDL吸附剂与单一亲水型磺酸基配基,单一疏水型胆固醇基吸附剂吸附量和亲和吸附系数的关系。对双亲型LDL吸附剂的吸附动力学进行了初步研究,在LDL溶液中,亲水型磺酸基,疏水型胆固醇配基,双亲型LDL吸附剂对LDL的吸附曲线基本上符合Langmuir吸附方程,另外通过高离子强度NaCl洗脱实验,测定了双亲型LDL吸附剂上具有的磺酸基与胆固醇两类基在对低密脂蛋白吸附过程中所起的配合效果,为下一步作用力机制研究提供了参考依据。 相似文献
995.
羧甲基壳聚糖/聚乙烯醇/甘油环氧树脂蛇笼型复合螯合膜的制备及对金属离子的吸附性能 总被引:4,自引:0,他引:4
以交联甘油环氧树脂交联的聚乙烯醇(PVA)为笼树脂,羧甲基壳聚糖(CCTS)为蛇树脂制备了具有蛇笼结构的复合螯合膜,研究了其对Cu^2 、Ni^2 、Pb^2 、Fe^3 、Zn^2 ,Hg”^2 、Cd^2 等金属离子的吸附性能,研究表明,该树脂对Cu^2 、Ni^2 、Pb^2 有较好的吸附性能,其中PVA是对Cu^2 的吸附的主要贡献者,而CCTS则是在对Ni^2 的吸附中起主要作用。该树脂可以用于含Cu^2 废水的处理。 相似文献
996.
FuShengWANG BingKuiSONG XiaoLiHAN BaoGuiZHANG 《中国化学快报》2004,15(12):1487-1490
Black lead, Ti-Ru and Ti-PbO2 were used as anode and stainless steel was used as cathode The electrolytic process of producing hypophosphorous acid with four-compartment electrodialytic cell was studied. The comparison of some factors, such as anodic voltage, product concentration and current efficiency, of black lead, Ti-Ru, and Ti-PbO2 electrodes was conducted. As a result, theTi-PbO2 electrode is the optimal anode material used, it can be in electrolytic process for producing hypophosphorous acid. 相似文献
997.
998.
999.
Qing Yan Li Hong Liang Hu Biao Chen Bin Wang Yu Ying Zhao 《中国化学快报》2007,18(7):843-845
One new cucurbitane-type triterpenoid saponin, 5b,19-epoxycucurbita-6,23-diene-3b,19,25-triol-3-O-b-D-allopyranoside (1), named momordicoside P was isolated from the fresh fruits of Momordica charantia. The structure of the saponin was elucidated byspectral methods, including 2D-NMR spectra. 相似文献
1000.
A series of new 2‐substituted 3‐(4‐chlorophenyl)‐5,8,9‐trimethylthieno[3′,2′: 5,6]pyrido[4,3‐d]pyrimidin‐4(3H)‐ones 8 were synthesized via an aza‐Wittig reaction. Phosphoranylideneamino derivatives 6a or 6b reacted with 4‐chlorophenyl isocyanate to give carbodiimide derivatives 7a or 7b , respectively, which were further treated with amines or phenols to give compounds 8 in the presence of a catalytic amount of EtONa or K2CO3. The structure of 2‐(4‐chlorophenoxy)‐3‐(4‐chlorophenyl)‐5,8,9‐trimethylthieno[3′,2′: 5,6]pyrido[4,3‐d]pyrimidin‐4(3H)‐one ( 8j ) was comfirmed by X‐ray analysis. 相似文献