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   9858篇
  免费   1872篇
  国内免费   1048篇
化学   6887篇
晶体学   88篇
力学   588篇
综合类   52篇
数学   1086篇
物理学   4077篇
  2024年   47篇
  2023年   237篇
  2022年   361篇
  2021年   417篇
  2020年   407篇
  2019年   383篇
  2018年   383篇
  2017年   315篇
  2016年   534篇
  2015年   461篇
  2014年   597篇
  2013年   789篇
  2012年   951篇
  2011年   907篇
  2010年   625篇
  2009年   610篇
  2008年   621篇
  2007年   534篇
  2006年   497篇
  2005年   404篇
  2004年   311篇
  2003年   234篇
  2002年   201篇
  2001年   173篇
  2000年   206篇
  1999年   221篇
  1998年   175篇
  1997年   162篇
  1996年   187篇
  1995年   144篇
  1994年   121篇
  1993年   91篇
  1992年   99篇
  1991年   56篇
  1990年   74篇
  1989年   55篇
  1988年   29篇
  1987年   28篇
  1986年   37篇
  1985年   39篇
  1984年   14篇
  1983年   17篇
  1982年   8篇
  1981年   4篇
  1980年   6篇
  1979年   2篇
  1977年   1篇
  1976年   2篇
  1957年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
In this paper, we study the Joule–Thomson expansion for RN-Ad S black holes immersed in perfect fluid dark matter. As perfect fluid dark matter is one of the dark matter candidates, we are interested in how it influences the thermodynamic properties of black holes. Firstly, the negative cosmological constant could be interpreted as thermodynamic pressure and its conjugate quantity as the thermodynamic volume, which give us more physical insights into the black hole. Moreover, we derive the thermodynamic definitions and study the critical behaviour of the black hole. Secondly,the explicit expression of Joule–Thomson coefficient is obtained from the basic formulas of the pressure, the volume, the entropy and the temperature. Then, we obtain the inversion curves in terms of charge Q and parameter λ. Furthermore, we analyse the isenthalpic curve in T–P graph with the cooling–heating region determined by the inversion curve. At last, we derive the ratio of minimum inversion temperature to critical temperature and compare the result with that in the RN-Ad S case.  相似文献   
902.
International Journal of Theoretical Physics - With entanglement-assisted (EA) formalism, arbitrary classical linear codes are allowed to transform into EAQECCs by using pre-shared entanglement...  相似文献   
903.

Importance of quantum entanglement has been demonstrated in various applications. Usually, separability of a bipartite state is defined by its algebraic structure, i.e. a convex combination of product states. But it seems to be hard to check separability (equivalently, entanglement) of a state from its algebraic structure. In this note, we give some characterizations of separability of bipartite states based on POVM measurements. For bipartite pure states, we prove the separability, Bell locality, unsteerability and classical correlation are the same. As a consequence, every entangled pure bipartite state is always Bell nonlocal, steerable and quantum correlated.

  相似文献   
904.
Quantum entanglement is regarded as one of the core concepts,which is used to describe the nonclassical correlation between subsystems,and entropic uncertainty relation plays a vital role in quantum precision measurement.It is well known that entanglement of formation can be expressed by von Neumann entropy of subsystems for arbitrary pure states.An interesting question is naturally raised:is there any intrinsic correlation between the entropic uncertainty relation and quantum entanglement?Or if the relation can be applied to estimate the entanglement.In this work,we focus on exploring the complementary relation between quantum entanglement and the entropic uncertainty relation.The results show that there exists an inequality relation between both of them for an arbitrary two-qubit system,and specifically the larger uncertainty will induce the weaker entanglement of the probed system,and vice versa.Besides,we use randomly generated states as illustrations to verify our results.Therefore,we claim that our observations might offer and support the validity of using the entropy uncertainty relation to estimate quantum entanglement.  相似文献   
905.
Verbenanone (1), a new secondary metabolite with a unique (4aS,8aS)-octahydro-5H-chromen-5-one moiety has been obtained from the endophytic fungus FT431, which was isolated from the native Hawaiian plant Verbena sp. The structure of compound 1 was characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of compound 1 was determined by Mosher acids. Compound 1 was tested against A2780 and A2780cisR, but it was inactive.  相似文献   
906.
Since the initial discovery of applications of platinum complexes in the clinical treatment of many kinds of cancers, the efficiency of platinum complexes in inhibiting the proliferation of various types of tumors surprised researchers working on the development of anticancer drugs. Meanwhile, despite the potent clinical treatment patients get from platinum complexes, there are also disadvantages including limited solubility in aqueous media and side effects like ototoxicity, myelosuppression, nephrotoxicity, and poor selectivity toward healthy cells. For this reason, efforts have been made to search for novel solutions. Non-platinum complexes (like Fe, Pd, Ru, Cu, Bi, Zn, etc.) were found with potential anticancer activities. We here review the properties of five metal complexes as anticancer agents and make comparisons among them in biological features and cytotoxic activity. Seeking the interrelation between microstructure and mechanism of anticancer, we hope this review provides distinct insights into future study of anticancer agents.  相似文献   
907.
908.
A field-portable device for logging PM2.5 mass concentration data has been developed. The device combines the Arduino microprocessor with an SD card, a Sharp DN7C3CA006 optical dust monitor, and 10,000-mAh battery. The dust sensor uses a virtual impactor to size select particles <2.5 microns prior to illuminating the selected fraction with an LED. The LED is triggered by a circuit controlled with the Arduino. Nephelometric detection at 120° referenced to incidence is used. The voltage signal reported by the dust sensor is converted to PM2.5 mass through calibration onboard the Arduino. Data points can be saved to the SD card as rapidly as 0.3?s, although averaging signals over 60?s produced more optimal detection limits. For a 60?s average, the PM2.5 mass limit of detection was 9?µg?m?3, indicating that the sensor will be useful for monitoring human exposure to fine particles. Portable exposure monitoring has been demonstrated with the sensing platform as several individuals carried the device with them during daily activities in Lubbock, TX and Atlanta, GA. For this group of test subjects, values of PM2.5 exposure varied from 0 to 1000?µg?m?3 during the sampling periods. It was observed that, by far, the highest levels of PM2.5 occur during periods of cooking, or being near cooking operations. Other periods of high PM2.5 occurred during ground transportation, use of personal care products, vacuuming, and visiting restrooms. When hourly personal exposure data were correlated with hourly average PM2.5 for outdoor air for the Atlanta data set, a very weak correlation was found (R2?=?0.026). Only two out of eight sampling periods did the personal monitoring estimate of exposure agree with that predicted by outdoor monitoring to within 15%. Personal exposure was often affected by circumstantial, short-term, high exposure events that are difficult to model or predict effectively. The short-term exposure events generally cause true exposure to be higher than that predicted by using outdoor ambient PM2.5 to generate estimates. This finding complicates interpretation of epidemiological studies that find links between ambient outdoor PM2.5 levels and human health, while it buttresses the case for using personal ambient monitors.  相似文献   
909.
910.
A one-pot, three-component reaction of aromatic aldehydes, 2-hydroxy-1,4-naphthoquinone, and 3,4-methylenedioxyphenol has been reported for the synthesis of novel 7-aryl-6H-benzo[h][1,3]dioxolo[4,5-b]xanthene-5,6(7H)-diones using environmentally benevolent para-toluene sulfonic acid (p-TSA) as the catalyst. This methodology provides a mild and fast route to diverse pyran derivatives in moderate to good yields.  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