全文获取类型
收费全文 | 139920篇 |
免费 | 18579篇 |
国内免费 | 12195篇 |
专业分类
化学 | 65900篇 |
晶体学 | 1015篇 |
力学 | 6091篇 |
综合类 | 604篇 |
数学 | 10900篇 |
物理学 | 39571篇 |
综合类 | 46613篇 |
出版年
2024年 | 648篇 |
2023年 | 2781篇 |
2022年 | 4317篇 |
2021年 | 4804篇 |
2020年 | 4698篇 |
2019年 | 3974篇 |
2018年 | 3798篇 |
2017年 | 3562篇 |
2016年 | 5360篇 |
2015年 | 5642篇 |
2014年 | 7142篇 |
2013年 | 8545篇 |
2012年 | 10101篇 |
2011年 | 10384篇 |
2010年 | 7457篇 |
2009年 | 7382篇 |
2008年 | 8087篇 |
2007年 | 7269篇 |
2006年 | 6541篇 |
2005年 | 5694篇 |
2004年 | 4387篇 |
2003年 | 3622篇 |
2002年 | 3685篇 |
2001年 | 3324篇 |
2000年 | 3059篇 |
1999年 | 4346篇 |
1998年 | 3879篇 |
1997年 | 3829篇 |
1996年 | 3667篇 |
1995年 | 3199篇 |
1994年 | 2786篇 |
1993年 | 2398篇 |
1992年 | 2115篇 |
1991年 | 1900篇 |
1990年 | 1624篇 |
1989年 | 1374篇 |
1988年 | 1088篇 |
1987年 | 759篇 |
1986年 | 552篇 |
1985年 | 356篇 |
1984年 | 172篇 |
1983年 | 129篇 |
1982年 | 103篇 |
1981年 | 60篇 |
1980年 | 43篇 |
1979年 | 16篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 32篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The prediction of the peak width at half height is an important aspect in the optimization of the chromatographic operating conditions. In this paper, a linear relationship, between the peak widths at half height and the retention values with various isocratic elution is observed. In gradient elution, however, the relationship between the peak widths at half height and the so-called invented retention values that correspond to the mobile phase composition by eluting the solute from the column end is developed. We believe that there is almost the same band width at half height inside the column (in unit of length) for different solutes. The peak width at half height in the chromatogram (in unit of time) is mainly determined by the capacity factor of the solute when it is eluted from the column end. The larger the capacity factor of a solute eluted from the column end, the more slowly will be the solute eluted from the column end and the wider will be the peak width at half height. It is possible to predict the peak width at half height in various isocratic and gradient elutions by using this linear relationship. 相似文献
102.
ICP方法匹配深度图像的实现 总被引:3,自引:0,他引:3
针对ICP(迭代最近点 )方法中寻找深度像之间点对应关系这一难点问题 ,首先介绍对ICP方法匹配深度图像的原理并给出单位四元数和旋转角度间的关系 ,然后提出一种验证两个深度图像中对应点对有效性的方法 ,给出了判断待匹配深度图像之间的点对应条件的准则 ,同时给出了实现这种准则的数据结构以及程序设计思想 .最后 ,用真实深度图像证明此方法的有效性 ,并用“主次缝合线”法合成匹配后的深度图像 相似文献
103.
本文给出了包含Fibonacci序列{Fn}、Lucas序列{Ln}及高阶Bernoulli多项式Bn(K)(x)的一些恒等式。 相似文献
104.
黄磷废水处理系统中氰降解菌的筛选 总被引:2,自引:0,他引:2
首次对含有氰化物的黄磷废水进行了氰降解菌筛选优化,共得耐氰菌20株,其中有9株的降氰率在90%以上,且AB2001003菌株降氰率在97.1%以上.该菌能在72 h内使含CN~-50mg·L~(-1)的黄磷废水降至0.5 mg·L~(-1)以下,达到国家一级排放标准.该菌的最佳生长pH7.7,最佳温29℃. 相似文献
105.
应用 ̄(45)Ca跨膜流动测定技术研究钙拮抗剂verapamil、中药西红花(CrocusSativusL.)、“地奥心血康”(DAXXK)、川红花(CarthamustinctoriusL.)及银杏叶(GinkgobilobaL.)等对大鼠主动脉 ̄(45)Ca跨膜内流的作用,以确定其对细胞膜Ca ̄(2+)通道影响。实验结果表明:西红花、川红花、DAXXK对平滑肌细胞膜上电压依赖Ca ̄(2+)通道(PDC)和受体操纵Ca ̄(2+)通道(ROC)都有阻滞作用,并以西红花的阻滞作用最强;而银杏叶对细胞膜Ca ̄(2+)通道无阻滞作用。 相似文献
106.
Orthogonally linear polarized lasers(Ⅰ)--principle and devices 总被引:1,自引:0,他引:1
Two kinds of orthogonally polarized lasers, i.e. Zeeman dual-frequency lasers and four-frequency ring lasers (laser gyros) have been developed since the invention of lasers, in which circularly polarized lights oscillate. This paper summarizes recent progress of the study on orthogonally linear polarized lasers with the standing wave cavity. Firstly, the expression of producing orthogonally linear polarized lights in standing wave cavity, i.e. laser frequency splitting, is given. Almost all the birefringence effects made in laser cavity are used to produce orthogonally linear polarized lights. The effect includes quartz crystal birefringence effect, calcite birefringence effect,stress (photo-elastic) birefringence effect and electro-optical birefringence effect. Secondly, several physical phenomena of orthogonally linear polarized lasers are discovered such as aberrance of frequency splitting curves caused by optical activity of quartz crystal, order-passing of longitudinal modes with frequency splitting and strong modes competition. Finally, because the traditional Zeeman dual frequency laser cannot output frequency difference larger than 3 MHz, the approaches of obtaining larger frequency difference are studied. The sequential results, several kinds of orthogonally polarized lasers, are described, such as birefringence dual frequency lasers outputting a frequency difference from 40 MHz to hundreds of megahertz, birefringence-Zeeman dual frequency lasers outputting a frequency difference from 1 MHz to hundreds of megahertz, the LD pumped YAG birefringence dual frequency laser outputting frequency difference of several gigahertz, and the lasers whose longitudinal mode spacing is c/4L instead of c/2L. 相似文献
107.
108.
A possible biological intermediate in the reduction and methylation of selenium oxyanions, dimethyl selenone, was synthesized, and the first experiments involving the amendment of selenium resistant bacterial cultures with this compound are reported. The amount of volatile, reduced selenium-containing species released from these cultures into the headspace is significantly more than that produced in analogous experiments involving sodium selenate amended cultures. Dimethyl selenone is reduced in the presence of dimethyl sulfide and dimethyl disulfide in a complex growth medium, trypticase soy broth with 0.1% nitrate. This reduction occurs whether or not the reduced sulfur compounds are biologically produced. 相似文献
109.
主要研究了处理含油污水用的聚砜超滤膜的分离、透过性能与制膜液配方(聚合物浓度、溶剂及添加剂的种类和配比)之间的关系.确定了最佳的制膜液配比.所制得的膜在操作压力为0.36MPa(绝)时,其纯水通量为750L/(m~2·h).处理含石油类36~100ppm的含油污水时透过液通量达130~355L/(m~2·h).透过液中含油量降至10ppm以下.透过液中的石油类、悬浮物及色度等都基本上达到国家排放标准及油田注水用标准. 相似文献
110.
本文阐述了煤矿井下排水设备的计算机辅助设计中选型程序的编制及绘图,介绍了程序的功能,若干技术问题的处理和绘图方法与要点. 相似文献