全文获取类型
收费全文 | 3700篇 |
免费 | 218篇 |
国内免费 | 316篇 |
专业分类
化学 | 2572篇 |
晶体学 | 79篇 |
力学 | 126篇 |
综合类 | 15篇 |
数学 | 568篇 |
物理学 | 874篇 |
出版年
2022年 | 41篇 |
2021年 | 65篇 |
2020年 | 68篇 |
2019年 | 53篇 |
2018年 | 55篇 |
2017年 | 52篇 |
2016年 | 82篇 |
2015年 | 89篇 |
2014年 | 83篇 |
2013年 | 197篇 |
2012年 | 203篇 |
2011年 | 212篇 |
2010年 | 154篇 |
2009年 | 157篇 |
2008年 | 245篇 |
2007年 | 221篇 |
2006年 | 248篇 |
2005年 | 194篇 |
2004年 | 153篇 |
2003年 | 127篇 |
2002年 | 125篇 |
2001年 | 66篇 |
2000年 | 74篇 |
1999年 | 59篇 |
1998年 | 56篇 |
1997年 | 42篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 35篇 |
1993年 | 41篇 |
1992年 | 48篇 |
1991年 | 40篇 |
1990年 | 31篇 |
1989年 | 44篇 |
1988年 | 36篇 |
1987年 | 24篇 |
1986年 | 28篇 |
1985年 | 43篇 |
1984年 | 48篇 |
1983年 | 37篇 |
1982年 | 47篇 |
1981年 | 55篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1978年 | 39篇 |
1977年 | 30篇 |
1976年 | 49篇 |
1975年 | 36篇 |
1974年 | 34篇 |
1973年 | 31篇 |
排序方式: 共有4234条查询结果,搜索用时 180 毫秒
1.
Henry Dring David Kreutzer Christoph Ritter Andreas Hilgeroth 《Molecules (Basel, Switzerland)》2021,26(1)
Despite the development of targeted therapies in cancer, the problem of multidrug resistance (MDR) is still unsolved. Most patients with metastatic cancer die from MDR. Transmembrane efflux pumps as the main cause of MDR have been addressed by developed inhibitors, but early inhibitors of the most prominent and longest known efflux pump P-glycoprotein (P-gp) were disappointing. Those inhibitors have been used without knowledge about the expression of P-gp by the treated tumor. Therefore the use of inhibitors of transmembrane efflux pumps in clinical settings is reconsidered as a promising strategy in the case of the respective efflux pump expression. We discovered novel symmetric inhibitors of the symmetric efflux pump MRP4 encoded by the ABCC4 gene. MRP4 is involved in many kinds of cancer with resistance to anticancer drugs. All compounds showed better activities than the best known MRP4 inhibitor MK571 in an MRP4-overexpressing cell line assay, and the activities could be related to the various substitution patterns of aromatic residues within the symmetric molecular framework. One of the best compounds was demonstrated to overcome the MRP4-mediated resistance in the cell line model to restore the anticancer drug sensitivity as a proof of concept. 相似文献
2.
Indermeet Kohli Taylor L. Braunberger Amanda F. Nahhas Fatima N. Mirza Mohsen Mokhtari Alexis B. Lyons Nikiforos Kollias Eduardo Ruvolo Henry W. Lim Iltefat H. Hamzavi 《Photochemistry and photobiology》2020,96(1):208-214
Human skin is exposed to visible light (VL; 400–700 nm) and long-wavelength ultraviolet A1 (UVA1) radiation (370–400 nm) after the application of organic broad-spectrum sunscreens. The biologic effects of these wavelengths have been demonstrated; however, a dose–response has not been investigated. Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated with 2 light sources (80–480 J cm−2): one comprising VL with less than 0.5% UVA1 (VL+UVA1) and the other pure VL. Skin responses were evaluated for 2 weeks using clinical and spectroscopic assessments. 4-mm punch biopsies were obtained from nonirradiated skin and sites irradiated with 480 J cm−2 of VL+UVA1 and pure VL 24 h after irradiation. Clinical and spectroscopic assessments demonstrated a robust response at VL+UVA1 sites compared with pure VL. Histology findings demonstrated a statistically significant increase in the marker of inflammation (P < 0.05) and proliferation (P < 0.05) at the irradiated sites compared with nonirradiated control. Threshold doses of VL+UVA1 resulting in biologic responses were calculated. Results indicate that approximately 2 h of sun exposure, which equates to VL+UVA1 dose (~400 J cm−2), is capable of inducing inflammation, immediate erythema and delayed tanning. These findings reinforce the need of photoprotection beyond the UV range. 相似文献
3.
Recursive algorithms for the computation of standard deviation and average deviation are derived and their applications in data acquisition are discussed. The relative speeds and accuracies of the two algorithms are compared for synthetic data. The performance of recursive estimation under shot and proportional noise limitations is also described. As an example of the utility of these algorithms, absorbance data with constant confidence intervals are collected regardless of incident and transmitted intensities. The desired precision is specified prior to data acquisition and used to control signal-averaging of the data in real time. 相似文献
4.
Clifford Henry Taubes 《Communications in Mathematical Physics》1989,122(3):455-526
A proof is given of Witten's conjectures for the rigidity of the index of the Dirac-Ramond operator on the loop space of a spin manifold which admits anS
1 symmetry.Research supported in part by the National Science Foundation 相似文献
5.
Henry P. McKean 《纯数学与应用数学通讯》2003,56(5):638-680
6.
A New Triterpene from the Orchid Pholidota yunnanensis 总被引:2,自引:0,他引:2
ZhiMingBI ZhengTaoWANG LuoShanXU 《中国化学快报》2004,15(10):1179-1181
A new triterpene, 25-methylenecyclopholidonyl p-hydroxy-trans-cinnamate, was isolated from a orchid Pholidota yunnanensis. The structure elucidation and ^1H, ^13C-NMR assignments were achieved by spectral and chemical method. 相似文献
7.
8.
利用球磨法制备石墨-六角氮化硼微晶混合物,并在6.1 GPa、800~1 500 ℃条件下与水进行高压反应,以便研究用水作触媒合成B-C-N三元化合物的可能性。通过对反应产物的XRD、XPS谱分析发现:高压下随着温度的升高,反应产物中出现再结晶石墨,其晶化程度逐渐提高;但没有出现再结晶六角氮化硼,也未出现立方氮化硼。在球磨不充分条件下,石墨-六角氮化硼混合物的XRD谱没有完全弥散,它们与水高压反应时,能观察到石墨与立方氮化硼分别结晶的现象,但都没有形成B-C-N晶化结构。 相似文献
9.
改进了张维迎对地区间竞争与国有企业民营化的分析,给出了经营者的剩余索取份额对竞争性的连续依赖关系:国有企业若要降低成本,就必须参与市场竞争,随着市场竞争的加强,国有企业经营者的剩余索取份额应该逐渐增大,而当市场竞争水平超过某一阈值,国有企业经营者拥有全部剩余索取权是最优的. 相似文献
10.
Realization of Greenberg-Horne-Zeilinger (GHZ) and W Entangled States with Multiple Superconducting Quantum-Interference Device Qubits in Cavity QED 下载免费PDF全文
An alternative scheme is proposed for generating the Greenberg-Horne-Zeilinger (GHZ) and W types of the entangled states with multiple superconducting quantum-interference device (SQUID) qubits in a single-mode microwave cavity field. In this scheme, there is no transfer of quantum information between the SQUIDs and the cavity, the cavity is always in the vacuum and thus the requirement on the quality of cavity is greatly loosened. In addition, during the process of the generation of the W entangled state, the present method does not involve a real excitation of intermediate levels. Thus, decoherence due to energy relaxation of intermediate levels is minimized. 相似文献