全文获取类型
收费全文 | 40789篇 |
免费 | 7022篇 |
国内免费 | 5054篇 |
专业分类
化学 | 28136篇 |
晶体学 | 556篇 |
力学 | 2622篇 |
综合类 | 374篇 |
数学 | 4649篇 |
物理学 | 16528篇 |
出版年
2024年 | 160篇 |
2023年 | 864篇 |
2022年 | 1609篇 |
2021年 | 1711篇 |
2020年 | 1764篇 |
2019年 | 1708篇 |
2018年 | 1538篇 |
2017年 | 1488篇 |
2016年 | 2063篇 |
2015年 | 2092篇 |
2014年 | 2504篇 |
2013年 | 3267篇 |
2012年 | 3770篇 |
2011年 | 3801篇 |
2010年 | 2637篇 |
2009年 | 2494篇 |
2008年 | 2763篇 |
2007年 | 2304篇 |
2006年 | 2073篇 |
2005年 | 1696篇 |
2004年 | 1309篇 |
2003年 | 1004篇 |
2002年 | 881篇 |
2001年 | 734篇 |
2000年 | 705篇 |
1999年 | 802篇 |
1998年 | 642篇 |
1997年 | 604篇 |
1996年 | 590篇 |
1995年 | 529篇 |
1994年 | 456篇 |
1993年 | 409篇 |
1992年 | 334篇 |
1991年 | 300篇 |
1990年 | 267篇 |
1989年 | 218篇 |
1988年 | 161篇 |
1987年 | 138篇 |
1986年 | 120篇 |
1985年 | 112篇 |
1984年 | 67篇 |
1983年 | 54篇 |
1982年 | 56篇 |
1981年 | 24篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1957年 | 12篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
YBa2Cu3O7-δ and Tl2Ba2CaCu2O8 thin films for microwave filters were synthesized by pulsed laser deposition and the two-step thalliation process. Substrate
quality requirements and the relation of thin film morphology, microstructure with microwave surface resistance were discussed. 相似文献
82.
Wei Zhou Ruonong Fu Rongji Dai Zaifu Huang Yanfei Chen 《Journal of separation science》1994,17(10):719-722
A new kind of side chain liquid crystalline polysiloxane containing a crown ether with a longer spacer (PSC-11) has been prepared and coated on a fused silica capillary column. The main chroma-tographic characteristics including efficiency, polarity, and selectivity have been examined. The phase exhibits the retention properties of both liquid crystal and crown ether stationary phases and possesses higher efficiency and better selectivity than PSC-3, which has a shorter spacer between the main polysiloxane chain and liquid crystalline side chain. 相似文献
83.
本利用矩阵给出了几类数列的通项公式的求法,把数列通项公式的求法转化为矩阵幂的计算,思路简单、计算简便,并能判别其敛散性。 相似文献
84.
THE ASYMPTOTIC SOLUTION FOR A CLASS OF SINGULARLY PERTURBED PROBLEM FOR SEMILINEAR SINGULAR EQUATION
The singularly perturbed boundary value problem for a class of semilinearsingular equation is considered. Using a simple and special method the asym-ptotic behavior of solution is studied. 相似文献
85.
86.
鲤鱼体中鱼腥味物质的提取和鉴定 总被引:2,自引:0,他引:2
采用同时蒸馏萃取法提取鲤鱼鱼体中的挥发和半挥发性有机物,用GC/MS从提取物中分析鉴定出鱼腥味和疑是鱼腥味物质16种。包括醛、烯醛、酮和呋喃4类化合物。其中己醛、庚醛和2,4-二烯癸醛被确认为鱼腥味的化合物。研究发现,这些物质总量在鲤鱼体的鱼鳞、鱼鳃和鱼肉的分布呈现下降趋势,且其总量与鱼腥味强度之间具有可比较的对应关系。 相似文献
87.
ZhengBin Zhang Chunying Liu Peifeng Li Zhenzhen Wu Cai Lin Huawei Huang Lei Xing Liansheng Liu 《Frontiers of Chemistry in China》2006,1(1):86-97
Many food algae and red tide algae were cultivated in the f/2 medium, and the nitric oxide (NO) concentration of the medium
and the cell density were determined. The experiments on algae were conducted when different concentrations of NO were added
into the medium using two methods. The results show that low concentrations of NO were self-produced by marine algae during
the exponential growth period and were about nmol/L level. But at the end of the period, i.e., 2 or 3 days before the cell
density reaches the maximum, an NO peak appeared, with the NO concentration reaching 10 nmol/L. The NO threshold concentration
exists according to the influence of exogenous NO on the marine phytoplankton growth. One type is the threshold concentration
that can promote algae growth, and its value is between 10 and 1 nmol level, or even lower. The other type can inhibit the
phytoplankton growth, which is about μmol level or higher. The results indicate that red tide algae are far more sensitive
to NO than are food algae. The fundamental experimental outcome above may provide a new clue for red tide chemical forecast
by inspecting the NO change. 相似文献
88.
We present a review of our recent measurements of total cross sections (Q
T's) for the scattering of positrons by Na, K, and Rb, and positronium-formation cross sections (Q
Ps's) for Na and K. For our total cross section measurements, a beam transmission technique has been used. For ourQ
Ps measurements, our approach involves setting upper and lower limits onQ
Ps using a combination of (1) measuring the transmission of the positron beam with the angular discrimination of the apparatus made as poor as possible, and (2) measuring the 511 keV annihilation gamma rays in coincidence produced by the decay of para-Ps formed in the scattering cell. Comparison with theoretical calculations shows that our measuredQ
T's andQ
Ps's for Na and K agree reasonably well with a close coupling approximation (CCA) calculation which takes into account the formation of Ps in then=1 andn=2 states. In the 3–10 eV energy range, this calculation predicts a peak in theQ
T's andQ
Ps's for K which also appears in our measurements. The absence of such a peak in our measuredQ
T's andQ
Ps's (preliminary) for Na in this energy range is also consistent with the same theory. Comparisons with five-state CCA calculations ofQ
T which do not take Ps-formation into account also show good agreement with our positron-Na, K, and RbQ
T measurements for energies above 20 eV, but show dramatic departures from our measurements below 10 eV for K and Rb. 相似文献
89.
90.
冠状动脉支架为圆柱形微型网状结构,直径1mm,厚度0.1mm,长度10~16mm。在经皮冠状动脉介入PCI治疗中由球囊充气撑开到直径为2.5~3.5mm的支架,在血管内承受血管壁回弹压力。为了保持血液流通支架必须保持其几何圆形。这是一个结构弹塑性稳定性问题。但是目前国际上对于支架的力学性能质量指标主要以强度性能评定而不涉及支架屈曲性能是不妥的。本文对于支架的强度和屈曲性能进行了全面的理论分析和实验研究,自行研制了智能式电子检测仪成功地对微型网状结构支架的强度和屈曲性能实现了实测实验研究。由于微型支架的离散型网状结构的特点,在实验中出现一些特殊的屈曲现象。本文研究结果对于支架的形状与性能设计的改进和力学性能质量标准规范的制订具有重要意义。 相似文献