全文获取类型
收费全文 | 321332篇 |
免费 | 20760篇 |
国内免费 | 11333篇 |
专业分类
化学 | 191935篇 |
晶体学 | 4319篇 |
力学 | 15575篇 |
综合类 | 593篇 |
数学 | 36023篇 |
物理学 | 104980篇 |
出版年
2022年 | 4691篇 |
2021年 | 5306篇 |
2020年 | 5920篇 |
2019年 | 5970篇 |
2018年 | 5963篇 |
2017年 | 5768篇 |
2016年 | 8723篇 |
2015年 | 7288篇 |
2014年 | 9407篇 |
2013年 | 16436篇 |
2012年 | 16733篇 |
2011年 | 18711篇 |
2010年 | 12786篇 |
2009年 | 12340篇 |
2008年 | 15018篇 |
2007年 | 14597篇 |
2006年 | 13559篇 |
2005年 | 12041篇 |
2004年 | 10040篇 |
2003年 | 8570篇 |
2002年 | 8255篇 |
2001年 | 8491篇 |
2000年 | 6689篇 |
1999年 | 5642篇 |
1998年 | 4817篇 |
1997年 | 4659篇 |
1996年 | 4852篇 |
1995年 | 4080篇 |
1994年 | 4138篇 |
1993年 | 3721篇 |
1992年 | 3868篇 |
1991年 | 3847篇 |
1990年 | 3471篇 |
1989年 | 3163篇 |
1988年 | 3007篇 |
1987年 | 2867篇 |
1986年 | 2886篇 |
1985年 | 3606篇 |
1984年 | 3592篇 |
1983年 | 2938篇 |
1982年 | 3176篇 |
1981年 | 2911篇 |
1980年 | 2678篇 |
1979年 | 2829篇 |
1978年 | 3021篇 |
1977年 | 3058篇 |
1976年 | 3087篇 |
1975年 | 2824篇 |
1974年 | 2945篇 |
1973年 | 2983篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
By optimizing pump power ratio between 1st order backward pump and 2nd order forward pump on discrete Raman amplifier, we demonstrated over 2dB noise figure improvement without excessive non-linearity degradation. 相似文献
992.
L. G. Lumbreras R. Gebhard W. Häusler F. Kauffmann-Doig J. Riederer G. Sieben U. Wagner 《Hyperfine Interactions》2003,150(1-4):51-72
Ceramic finds from the Galería de las Ofrendas at Chavín de Huántar and surface finds from the settlement of Chavín were characterised by combining the results of archaeological typology with archaeometric studies using neutron activation analysis, Mössbauer spectroscopy, X-ray diffraction and thin-section microscopy. Sherds from the pyramid Tello are included in the study as representative of local material. The analyses show that the vessels were made from different raw materials and that different firing procedures were used in their production. Sherds of certain styles largely exhibit similar types of Mössbauer patterns and in many instances also have similar element compositions. This supports the archaeological notion that the vessels were brought to Chavín from the provinces, perhaps on the occasion of a festivity. 相似文献
993.
In a Young–Michelson tandem interferometer a Michelson interferometer is illuminated through a pair of Young slits. The pattern produced by this set-up is analyzed theoretically. The consequences of small misalignments and uncompensated arms in the Michelson interferometer are studied. The effects of the spatial and temporal partial coherence of the source are also explored. Experimental results using a laser source are shown to be in good agreement with the predicted theoretical calculations. 相似文献
994.
995.
用溶胶 凝胶法以磷钼酸 (MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2 催化剂 .使用ICP、XRD、TG DTA、IR、TPD MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能 .杂多钼酸盐与TiO2 通过O2 -在TiO2 表面发生了键合 .在 6 2 3K下 ,杂多阴离子仍保持原有的Keggin结构 .CO2 在Lewis酸位Ni(Ⅱ )和Lewis碱位Ni-O -Mo的桥氧协同作用下生成CO2 卧式吸附态Ni(Ⅱ )←O - (CO)← (O--Ni) .丙烯有多种吸附态在催化剂上吸附 .在 5 6 3K、1MPa和空速 15 0 0h-1的反应条件下 ,丙烯的摩尔转化率为 3.2 % ,产物MAA选择性为 95 % . 相似文献
996.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献
997.
Qingfa Wang Li Wang Yaquan Wang Fei He Zhenhua Li Zhentao Mi 《Reaction Kinetics and Catalysis Letters》2004,81(2):297-304
Deactivated palladium catalysts in the hydrogenation of anthraquinione were regenerated with ethanol, nitric acid, hydrogen
peroxide, boiling water and steam, respectively. The deactivated and regenerated catalysts were characterized by XPS, ICP,
TG, FTIR, TPD, XRD, etc., and studied in the hydrogenation of anthraquinone. The results showed that the main cause of catalyst deactivation is the
coverage of the active component by deposits. The treatments by hydrogen peroxide and boiling water can effectively regenerate
the deactivated catalysts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
998.
999.
L. D. Popov 《Central European Journal of Mathematics》2004,2(1):76-86
For a linear complementarity problem with inconsistent system of constraints a notion of quasi-solution of Tschebyshev type
is introduced. It’s shown that this solution can be obtained automatically by Lemke’s method if the constraint matrix of the
original problem is copositive plus or belongs to the intersection of matrix classes P
0 and Q
0. 相似文献
1000.
L. A. Beklaryan 《Journal of Mathematical Sciences》2004,124(4):5098-5109
In the paper we study infinite-dimensional dynamic systems with the Frenkel–Kontorova potentials. For such systems we describe their traveling-wave-type solutions, which are solutions for the corresponding boundary-value problem with nonlocal conditions. Describing the mentioned solutions is equivalent to describing the space of solutions for a functional differential equation that can be canonically derived from the original dynamic system. The stability of traveling-wave-type solutions is also investigated. 相似文献