首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   14132篇
  免费   2449篇
  国内免费   2640篇
化学   6831篇
晶体学   428篇
力学   513篇
综合类   185篇
数学   1205篇
物理学   3774篇
无线电   6285篇
  2024年   65篇
  2023年   248篇
  2022年   572篇
  2021年   593篇
  2020年   486篇
  2019年   485篇
  2018年   485篇
  2017年   610篇
  2016年   581篇
  2015年   755篇
  2014年   879篇
  2013年   1099篇
  2012年   1222篇
  2011年   1306篇
  2010年   1158篇
  2009年   1220篇
  2008年   1274篇
  2007年   1130篇
  2006年   998篇
  2005年   855篇
  2004年   642篇
  2003年   475篇
  2002年   366篇
  2001年   405篇
  2000年   373篇
  1999年   179篇
  1998年   93篇
  1997年   87篇
  1996年   82篇
  1995年   64篇
  1994年   75篇
  1993年   44篇
  1992年   48篇
  1991年   39篇
  1990年   31篇
  1989年   41篇
  1988年   25篇
  1987年   22篇
  1986年   20篇
  1985年   11篇
  1984年   16篇
  1983年   12篇
  1982年   6篇
  1981年   10篇
  1980年   5篇
  1979年   10篇
  1978年   2篇
  1973年   3篇
  1964年   2篇
  1935年   1篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
111.
AFacileSynthesisofindolizinesby1,3-DipolarCycloadditionofPyridiniumandRelatedHeteroaromaticYlideswithAlkenesinthePresenceofTP...  相似文献   
112.
甲基橙亚硝化极谱法测定亚硝酸根   总被引:24,自引:0,他引:24  
研究了甲基橙亚硝化产物的极谱波行为 ,提出了亚硝化极谱法测定亚硝酸根的灵敏极谱波新体系。在 0 .6mol/L 盐酸中 ,甲基橙与 NO-2 的亚硝化反应产物在极谱仪上于 - 0 .31 V( vs.SCE)可获得灵敏的极谱波。导数波高与亚硝酸根浓度在 1 .0 9× 1 0 -7~ 1 .0 9× 1 0 -5mol/L范围内成正比 ,检出限为 6.52× 1 0 -8mol/L。研究了极谱波行为及反应机理。并利用该法测定了水样中的亚硝酸根  相似文献   
113.
The chemical compositions of silicate minerals, sulphide minerals and metal Fe-Ni in theQingzhen meteorite were measured by the microprobe analyses. Based upon these chemicalcompositions, the cosmochemical behaviour and characteristics of the existing forms of themajor elements in the Qinzhen meteorite have been discussed. These characteristics show thatunder the S-rich, O-poor, and strongly reducing conditions, the light metal elements, such asCa, Mg, K, Na may form sulphide, and metal Fe-Ni may contain Si and P. However, we con-sider that the light metal-sulphide can be stable in the lower mantle and there are some Siand P in the Fe-Ni core. Finally, an earth core-mantle model is established, where the Fe-Ni core contains some Si and P; the lower mantle is composed of Mg-rich silicate, SiO_2 andsulphide; the upper mantle, of silicate and oxide.  相似文献   
114.
115.
制备了一种新型的聚苯乙烯纳米纤维, 将其作为固相萃取吸附剂装填制成固相萃取柱, 与高效液相色谱联用建立了干辣椒、 水果饮料及红酒中罗丹明B的定量分析方法. 高效液相色谱以3 g/L磷酸缓冲液-甲醇混合溶液(体积比3∶7, pH=7.0)为流动相. 通过对提取条件的优化, 得到该方法对干辣椒中罗丹明B的检出限为0.1 ng/g, 最低定量限为0.6 ng/g; 对水果饮料和红酒中罗丹明B的检出限均为0.2 ng/mL, 最低定量限均为0.5 ng/mL. 此方法对干辣椒中罗丹明B的提取回收率为98.2%~110.3%; 对水果饮料中罗丹明B的提取回收率为94.6%~102.2%; 对红酒中罗丹明B的提取回收率为90.4%~104.6%. 该方法的线性范围为1~100 ng/mL(ng/g), 相对标准偏差为2.3%~9.0%. 该方法灵敏度高、 选择性好, 可用于干辣椒、 水果饮料及红酒中罗丹明B的定量分析.  相似文献   
116.
Development of highly functional cesium selective adsorbents for the decontamination of high-activity-level water(HALW) from the Fukushima NPP-1 accident is very urgent. In order to selectively adsorb the radioactive cesium, three kinds of novel porous silica gels loaded with insoluble ferrocyanides(SLFC) were prepared using a successive impregnation/precipitation method. Based on the results of previous research, the SLFC composites have relatively large uptake ratio above 95%, distribution coefficients(Kd) above 103 cm3/g, and excellent adsorption kinetics even in seawater. The solidification results also indicate that zeolites have an excellent Cs immobilization characteristic, gas-trapping and self-sintering abilities, and low leachability. We chose three kinds of SLFC composites to achieve the optimization of solidification by mixing with nine kinds of additives at high temperatures(up to 1200 °C). The Cs contents in the three composites were estimated to be below 30% of the initial contents and decreased with the three stages at calcination temperatures ranging from 25 to 1200 °C. By contrast, the Cs immobilization ratio was markedly lowered by mixing with additives: of those, allophane had the best immobilization result. By increasing the additive ratio to 50 wt%, the Cs immobilization ratio became almost 100% and no volatilization of Cs was detected even after calcination at 1200 °C. This result indicates that calcination of the mixture of SLFC composites after adsorbing Cs+ ions and specific additives under appropriate ratio is effective for stable solidification.  相似文献   
117.
Recently, PtIV prodrugs have attracted much attention as the next generation of platinum‐based antineoplastic drug candidates. Here we report the discovery and evaluation of monochalcoplatin, a monocarboxylated PtIV prodrug that is among the most cytotoxic PtIV prodrugs to date. Compared with its dicarboxylated counterpart chalcoplatin, monochalcoplatin accumulates astonishingly effectively and rapidly in cancer cells, which is not ascribed to its lipophilicity. The prodrug is quickly reduced, causes DNA damage, and induces apoptosis, resulting in superior cytotoxicity with IC50 values in the nanomolar range in both cisplatin‐sensitive and ‐resistant cells; these IC50 values are up to 422‐fold higher than that of cisplatin. A detailed mechanistic study reveals that monochalcoplatin actively enters cells through a transporter‐mediated process. Moreover, monochalcoplatin shows significant antitumor activity in an in vivo colorectal tumor model. Our study implies a practical strategy for the design of more effective PtIV prodrugs to conquer drug resistance by tuning both cellular uptake pathways and activation processes.  相似文献   
118.
Matrix solid-phase dispersion(MSPD) was developed for the extraction of four alkaloids, including aconitine, mesaconitine, hypaconitine and deoxyaconitine, from the roots of Aconitum kusnezoffii Reichb. The determination of the analyte was carried out by high performance liquid chromatography with UV detection. The alkaline alumina was used as sorbent. The mixture of acetonitrile and water was used as elution solvent. Several extraction parameters, such as type of sorbent, the ratio of sample to solid suppo...  相似文献   
119.
120.
用GDS-7600凝胶成像分析系统对蛋白质凝胶电泳板进行了成像和分析,然后再将图像、图表通过计算机处理插入到word文档中并编辑为word文档的内容。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号