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   23530篇
  免费   4208篇
  国内免费   3404篇
化学   10703篇
晶体学   294篇
力学   1014篇
综合类   235篇
数学   1767篇
物理学   6720篇
无线电   10409篇
  2024年   134篇
  2023年   525篇
  2022年   821篇
  2021年   981篇
  2020年   955篇
  2019年   877篇
  2018年   842篇
  2017年   868篇
  2016年   1035篇
  2015年   1225篇
  2014年   1508篇
  2013年   1792篇
  2012年   2152篇
  2011年   2108篇
  2010年   1736篇
  2009年   1749篇
  2008年   1836篇
  2007年   1666篇
  2006年   1534篇
  2005年   1283篇
  2004年   950篇
  2003年   695篇
  2002年   652篇
  2001年   600篇
  2000年   538篇
  1999年   401篇
  1998年   241篇
  1997年   202篇
  1996年   187篇
  1995年   139篇
  1994年   145篇
  1993年   116篇
  1992年   122篇
  1991年   92篇
  1990年   90篇
  1989年   61篇
  1988年   53篇
  1987年   34篇
  1986年   33篇
  1985年   31篇
  1984年   30篇
  1983年   21篇
  1982年   15篇
  1981年   13篇
  1980年   5篇
  1979年   7篇
  1974年   5篇
  1966年   7篇
  1964年   4篇
  1960年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Commonly used clinical chemotherapy drugs, such as cyclophosphamide (CTX), may cause injury to the ovaries. Hormone therapies can reduce the ovarian injury risk; however, they do not achieve the desired effect and have obvious side effects. Therefore, it is necessary to find a potential therapeutic candidate for ovarian injury after chemotherapy. N-Benzyl docosahexaenamide (NB-DHA) is a docosahexaenoic acid derivative. It was recently identified as the specific macamide with a high degree of unsaturation in maca (Lepidium meyenii). In this study, the purified NB-DHA was administered intragastrically to the mice with CTX-induced ovarian injury at three dose levels. Blood and tissue samples were collected to assess the regulation of NB-DHA on ovarian function. The results indicated that NB-DHA was effective in improving the disorder of estrous cycle, and the CTX+NB-H group can be recovered to normal levels. NB-DHA also significantly increased the number of primordial follicles, especially in the CTX+NB-M and CTX+NB-H groups. Follicle-stimulating hormone and luteinizing hormone levels in all treatment groups and estradiol levels in the CTX+NB-H group returned to normal. mRNA expression of ovarian development-related genes was positive regulated. The proportion of granulosa cell apoptosis decreased significantly, especially in the CTX+NB-H group. The expression of anti-Müllerian hormone and follicle-stimulating hormone receptor significantly increased in ovarian tissues after NB-DHA treatment. NB-DHA may be a promising agent for treating ovarian injury.  相似文献   
72.
Estrogens added illegally to dietary supplements are hazardous to human health. Traditional detection and analysis methods have many limitations, and we have developed an assay that combines thin-layer chromatography with Raman imaging microscopy (TLC-RIM). The five estrogens (estrone, estradiol, estriol, ethinyl estradiol, and diethylstilbestrol) were initially separated by TLC, then detected by area scanning Raman imaging with a 532 nm laser under a microscope. Raman spectra were obtained for each estrogen, which were used for detecting estrogen illegally added to botanical dietary supplements. The LOD of each estrogen was 0.4, 1.0, 0.8, 0.2, and 0.2 mg/mL, respectively. The matrix in the real sample did not interfere with the detection of estrogens. The method was fast, sensitive, stable, specific, and reliable.  相似文献   
73.
高导电性ZAO陶瓷靶材及薄膜的制备   总被引:8,自引:1,他引:8  
用热等静压法烧结制备了高导电性ZAO(铝掺杂氧化锌)陶瓷靶材,并用直流磁控溅射法制备出ZAO透明导电薄膜。靶材的致密度达98.7%,电阻率为2.2?03·cm;制得薄膜的最低电阻率为9.3?04·cm,可见光平均透射率大于85%。浅析了靶材的组织结构及靶材的电学、力学性能和薄膜制备的主要实验参数对其光、电性能的影响。  相似文献   
74.
作为一种原位、快速、无损坏的中红外光谱分析技术,ATR-FTIR已在很多工程领域得到越来越多的应用,尤其是针对结晶过程溶液浓度的原位实时测量。水是一种常用的结晶溶剂,在中红外波段具有强吸收峰,并且在不同温度下具有光谱吸收差异性,因而不能忽略溶剂水和温度对溶液浓度的中红外光谱测量带来的影响。以朗伯-比尔定律为基础,提出采用溶液光谱减去相应温度下的溶剂光谱的方法,从而能准确地测量溶液浓度。以L-谷氨酸溶液结晶过程为例,对L-谷氨酸水溶液的原始光谱数据、溶液光谱扣除常温(25℃)溶剂水的光谱数据以及溶液光谱对应温度扣除溶剂水的光谱数据分别进行建模。结果表明,提出的对应温度差谱法能有效消除溶剂水峰对溶质光谱测量的干扰,明显地降低了溶液浓度光谱标定模型的预测误差。该方法对提高原位ATR-FTIR光谱检测精度的实际应用具有一定的参考价值。  相似文献   
75.
The effect of H impurity on the misfit dislocation in Ni-based single-crystal superalloy is investigated using the molecular dynamic simulation.It includes the site preferences of H impurity in single crystals Ni and Ni 3 Al,the interaction between H impurity and the misfit dislocation and the effect of H impurity on the moving misfit dislocation.The calculated energies and simulation results show that the misfit dislocation attracts H impurity which is located at the γ/γˊinterface and Ni3 Al and H impurity on the glide plane can obstruct the glide of misfit dislocation,which is beneficial to improving the mechanical properties of Ni based superalloys.  相似文献   
76.
陶理  迟楠 《光学学报》2012,32(4):406003-75
提出了一种新型的基于串行结构的最小频移键控调制技术,产生了相位连续,频谱宽度窄,每码元时间有两次π/2相移,类似于传统最小频移键控调制信号,给出了该调制方案的理论推导,并将其应用于8进制的多维多阶调制系统中。理论和仿真分析了不同的8进制调制方案在频谱特性,残留色散容限,自相位调制容限的不同,还分析了其受到系统滤波带宽的影响。最后仿真实现了通过350km的色散完全补偿的光纤120Gb/s的数据传输。  相似文献   
77.
The construction of maximally entangled bases for the bipartite system \(\mathbb {C}^{d}\otimes \mathbb {C}^{d}\) is discussed firstly, and some mutually unbiased bases with maximally entangled bases are given, where 2≤d≤5. Moreover, we study a systematic way of constructing mutually unbiased maximally entangled bases for the bipartite system \(\mathbb {C}^{d}\otimes \mathbb {C}^{d^{k}}\).  相似文献   
78.
提出了一种原子荧光光谱法间接测定中草药中铜含量的方法。在弱酸性介质中,CuI与HgI42-反应生成稳定的Cu2HgI4,经异戊醇萃取分离后,通过用原子荧光光谱法测定有机相中剩余的汞量,间接换算成铜含量。铜的质量浓度在0.01~0.1mg.L-1范围内与荧光强度呈线性关系,方法的检出限(3S/N)为3.5μg.L-1。方法用于国家标准物质黄芪(GSB-19)、茶叶(GSB-7)和柑橘叶(GSB-11)的分析,测定值与认定值相符,测定值的相对标准偏差(n=9)在0.8%~2.4%之间。  相似文献   
79.
80.
Surfaces of three types of CuZr-based bulk metallic glasses (BMGs) were modified by laser surface treatment (LST), and the influence of the treatment on structure and mechanical properties of these alloys was investigated. The phase structure of as-cast and laser-treated samples was characterized by XRD and the morphology of the alloys after fracture was examined by SEM. The compressive plasticity of treated Cu47.5Zr47.5Al5 and Cu46.5Zr47.5Al5Co1 BMGs can be improved from 0.5% to 2.0% and from 1.2% to 5.7% respectively compared with the as-cast ones, while (Cu0.55Zr0.40Al0.05)99Er1 BMG shows insignificant change of plasticity. The improvement in plasticity is attributed to induced crystallization of B2 CuZr phase in the treated surface zone of selected metallic glasses.  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