全文获取类型
收费全文 | 13504篇 |
免费 | 376篇 |
国内免费 | 46篇 |
专业分类
化学 | 10811篇 |
晶体学 | 73篇 |
力学 | 210篇 |
数学 | 1667篇 |
物理学 | 1165篇 |
出版年
2023年 | 107篇 |
2022年 | 447篇 |
2021年 | 506篇 |
2020年 | 282篇 |
2019年 | 330篇 |
2018年 | 253篇 |
2017年 | 213篇 |
2016年 | 434篇 |
2015年 | 441篇 |
2014年 | 417篇 |
2013年 | 832篇 |
2012年 | 858篇 |
2011年 | 972篇 |
2010年 | 588篇 |
2009年 | 579篇 |
2008年 | 820篇 |
2007年 | 800篇 |
2006年 | 683篇 |
2005年 | 621篇 |
2004年 | 526篇 |
2003年 | 442篇 |
2002年 | 432篇 |
2001年 | 168篇 |
2000年 | 136篇 |
1999年 | 112篇 |
1998年 | 115篇 |
1997年 | 100篇 |
1996年 | 129篇 |
1995年 | 90篇 |
1994年 | 87篇 |
1993年 | 80篇 |
1992年 | 65篇 |
1991年 | 77篇 |
1990年 | 57篇 |
1989年 | 79篇 |
1988年 | 65篇 |
1987年 | 53篇 |
1986年 | 56篇 |
1985年 | 66篇 |
1984年 | 94篇 |
1983年 | 48篇 |
1982年 | 73篇 |
1981年 | 61篇 |
1980年 | 55篇 |
1979年 | 47篇 |
1978年 | 55篇 |
1977年 | 40篇 |
1976年 | 36篇 |
1975年 | 27篇 |
1963年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Renata Monteiro-Maia Maria B Ortigão-de-Sampaio Rosa T Pinho Luiz RR Castello-Branco 《Journal of immune based therapies and vaccines》2006,4(1):1-6
We hypothesize that the energy strategy of a cell is a key factor for determining how, or if, the immune system interacts
with that cell. Cells have a limited number of metabolic states, in part, depending on the type of fuels the cell consumes.
Cellular fuels include glucose (carbohydrates), lipids (fats), and proteins. We propose that the cell's ability to switch
to, and efficiently use, fat for fuel confers immune privilege. Additionally, because uncoupling proteins are involved in
the fat burning process and reportedly in protection from free radicals, we hypothesize that uncoupling proteins play an important
role in immune privilege. Thus, changes in metabolism (caused by oxidative stresses, fuel availability, age, hormones, radiation,
or drugs) will dictate and initiate changes in immune recognition and in the nature of the immune response. This has profound
implications for controlling the symptoms of autoimmune diseases, for preventing graft rejection, and for targeting tumor
cells for destruction. 相似文献
132.
Maria Rivera-Araya Kitty F. Emery M. Charlotte Arnauld Suzanne Pilaar Birch 《Isotopes in environmental and health studies》2013,49(4):344-365
ABSTRACTCarbon and oxygen isotopes ratios from herbivore teeth have previously been used as paleo-environmental proxies in temperate zones. However, their utility in tropical zones remains uncertain. In this study, sequential sub-samples from white-tailed deer (Odocoileus virginianus) teeth (second and third molars) from the Maya archaeological site of La Joyanca, located in northwestern Petén, Guatemala, show that δ18O of enamel carbonate corresponds broadly to modern observed precipitation δ18O over the 10-month period of tooth formation, capturing rainfall seasonality. The analyses also detect significant diachronic differences in the δ18O between the periods 1100–1000 BP (850–950 A.D.) and 1000–900 BP (950–1050 A.D.) at La Joyanca. The δ13C in both periods are indicative of a C3-plant based diet, which suggests cultivation of maize did not differentially affect deer diet during this period. 相似文献
133.
Lenize F. Maia Vanessa E. de Oliveira Maria E. R. Oliveira Felipe D. Reis Beatriz G. Fleury Howell G. M. Edwards Luiz F. C. de Oliveira 《Journal of Raman spectroscopy : JRS》2013,44(4):560-566
Polyenic pigments in octocorals have been investigated by Raman spectroscopy using laser excitation at 532, 785 and 1064 nm. The spectral features suggest the structural nature of carotenoids from Phyllogorgia dilatata, Leptogorgia punicea, Muricea atlantica, Carijoa riisei and conjugated polyenals from L. punicea, L. setacea, Muricea flamma and Renilla muelleri. The observed vibrational bands at ca. 1540–1520 ν1(C=C), 1159 ν2(C–C) and 1005 cm−1 ρ3(C–CH3) were assigned to carotenoids, whereas the identification of non‐methylated conjugated polyenals have been proposed due to two major Raman bands at ca. 1500 and 1120 cm‐1, assigned to ν(C=C) and ν(C–C), respectively. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
134.
Pier?Paolo?ProsiniEmail author Maria?Carewska Gabriele?Tarquini Fabio?Maroni Agnese?Birrozzi Francesco?Nobili 《Ionics》2016,22(4):515-528
This paper describes the preparation and characterization of a high-voltage lithium-ion battery based on Sn-decorated reduced graphene oxide and LiNi0.5Mn1.5O4 as the anode and cathode active materials, respectively. The Sn-decorated reduced graphene oxide is prepared using a microwave-assisted hydrothermal synthesis method followed by reduction at high temperature of a mixture of (C6H5)2SnCl2 and graphene oxide. The so-obtained anode material is characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and electron diffraction spectroscopy. The LiNi0.5Mn1.5O4 is a commercially available product. The two materials are used to prepare composite electrodes, and their electrochemical properties are investigated by galvanostatic charge/discharge cycles at various current densities in lithium cells. The electrodes are then used to assemble a high-voltage lithium-ion cell, and the cell is tested to evaluate its performance as a function of discharge rate and cycle number. 相似文献
135.
136.
Yanpeng Xue Eirini Maria Paschalidou Paola Rizzi Livio Battezzati Hans-Jörg Fecht 《哲学杂志》2018,98(30):2769-2781
Nanoporous gold thin films have been fabricated through chemical de-alloying of Au-based nanoglass with a nanocolumnar structure, with composition Au40Cu28Ag7Pd5Si20 (at.%), that had previously been deposited by magnetron sputtering. By varying the de-alloying conditions, gold ligaments ranging from 20 to 100?nm were obtained. The microstructure and chemical composition of the as-prepared films were characterised by various techniques. Surface-enhanced Raman scattering (SERS) of thin films was investigated using rhodamine 6G. The results indicate that the main microstructural features with interconnected ligaments and defects of nanoporous gold result in significant SERS enhancement. 相似文献
137.
138.
139.
Flávia R. O. Silva Camila T. Nabeshima Maria H. Bellini Nestor Schor Nilson D. Vieira Jr Lilia C. Courrol 《Journal of fluorescence》2013,23(1):131-135
This paper describes the elimination of porphyrins by feces. It was demonstrated that porphyrin accumulates substantially more in tumors than in normal tissues, and consequently more PPIX reaches the blood of patients and animals with tumors, and then, it needs to be eliminated. The fluorescence of feces revealed that there are large amounts of PPIX in the excreta of animals with cancer comparing with healthy animals. The autofluorescence of feces porphyrin extracted with acetone was analyzed using fluorescence spectroscopy of animals inoculated with DU145 cells into the prostate and healthy animals to monitor the PPIX concentration. Emission spectra were obtained by exciting the samples at 405 nm. Significant differences were observed in autofluorescence intensities measured in the 575–725 nm spectral regions for the studied groups. The results showed a noninvasive, simple, rapid and sensitive method to detect cancer by feces analysis. 相似文献
140.
Aequationes mathematicae - The Hardy–Littlewood–Pólya inequality of majorization is extended for $$\mathbf {\omega }$$ – $$\textbf{m}$$ –star-convex functions to the... 相似文献