全文获取类型
| 收费全文 | 17705篇 |
| 免费 | 296篇 |
| 国内免费 | 386篇 |
专业分类
| 化学 | 2782篇 |
| 晶体学 | 96篇 |
| 力学 | 192篇 |
| 综合类 | 125篇 |
| 数学 | 13882篇 |
| 物理学 | 1310篇 |
出版年
| 2024年 | 30篇 |
| 2023年 | 52篇 |
| 2022年 | 182篇 |
| 2021年 | 141篇 |
| 2020年 | 127篇 |
| 2019年 | 392篇 |
| 2018年 | 451篇 |
| 2017年 | 224篇 |
| 2016年 | 195篇 |
| 2015年 | 219篇 |
| 2014年 | 453篇 |
| 2013年 | 1088篇 |
| 2012年 | 651篇 |
| 2011年 | 1001篇 |
| 2010年 | 927篇 |
| 2009年 | 1159篇 |
| 2008年 | 1176篇 |
| 2007年 | 1117篇 |
| 2006年 | 845篇 |
| 2005年 | 585篇 |
| 2004年 | 497篇 |
| 2003年 | 462篇 |
| 2002年 | 401篇 |
| 2001年 | 401篇 |
| 2000年 | 451篇 |
| 1999年 | 483篇 |
| 1998年 | 462篇 |
| 1997年 | 399篇 |
| 1996年 | 361篇 |
| 1995年 | 354篇 |
| 1994年 | 361篇 |
| 1993年 | 332篇 |
| 1992年 | 283篇 |
| 1991年 | 193篇 |
| 1990年 | 190篇 |
| 1989年 | 196篇 |
| 1988年 | 132篇 |
| 1987年 | 126篇 |
| 1986年 | 139篇 |
| 1985年 | 147篇 |
| 1984年 | 175篇 |
| 1983年 | 90篇 |
| 1982年 | 146篇 |
| 1981年 | 111篇 |
| 1980年 | 128篇 |
| 1979年 | 100篇 |
| 1978年 | 108篇 |
| 1977年 | 56篇 |
| 1976年 | 29篇 |
| 1975年 | 20篇 |
排序方式： 共有10000条查询结果，搜索用时 0 毫秒
101.
对湛江产芥菜,芫荽和麦菜的微量元素,氨基酸进行了定量分析。结果表明营养元素如Ｃｕ、Ｚｎ、Ｆｅ、Ｃａ、Ｍｇ、Ｋ、Ｍｎ、Ｎａ等的含量较丰富,也含有多种人体必需的氨基酸,但共同的特征是均缺乏赖氨酸。 相似文献
102.
We consider a catalytic branching Brownian motion with general branching which takes place only when particles are at the origin at a rate β>0 on the local time scale. We first establish a spine decomposition for the case wherein the particles have a positive probability of having no children. Then using this tool, we obtain results regarding the asymptotic behavior of the number of particles above λt at time t for λ>0. Under an L log L condition, we prove a strong law of large numbers for this catalytic branching Brownian motion. 相似文献
103.
104.
Natalizia Miceli Andreana Marino Ayşegül Köroğlu Francesco Cacciola Paola Dugo Luigi Mondello 《Natural product research》2020,34(11):1636-1641
AbstractThe purpose of this study was to conduct a comparative evaluation of some biological properties of methanol and water extracts of leaves of five Juniperus taxa growing in Turkey: J. communis L. var. communis (Jcc), J. communis L. var. saxatilis Pall. (Jcs), J. drupacea Labill. (Jd), J. oxycedrus L. subsp. oxycedrus (Joo), J. oxycedrus L. subsp. macrocarpa (Sibth. & Sm.) Ball. (Jom). The antioxidant properties were examined in vitro; both in the DPPH and in the reducing power tests, Joo methanol extract resulted the most active (IC50?=?0.09?±?0.01mg/mL and ASE/mL?=?2.56?±?0.06). In the TBA assay, Jcs methanol extract exhibited the highest activity (IC50?=?4.39?±?0.47?μg/mL). The extracts displayed bacteriostatic activity against Staphylococcus aureus, and Jd methanol extract resulted the most effective (MIC?=?19.53?μg/mL); no effect on the S. aureus biofilm formation was observed. The extracts resulted non-toxic in the Artemia salina lethality bioassay. Finally, the phenolic profile of the methanol extracts was characterized by HPLC-PDA/ESI-MS. 相似文献
105.
Ahmed Ashour Yhiya Amen Toshinori Nakagawa Yasuharu Niwa Amira Mira Koichiro Ohnuki 《Natural product research》2020,34(12):1750-1755
AbstractAn aliphatic ester of hydroxysalicylic acid (6), reported for the first time from a natural source in addition to five known compounds were isolated from the fermented Carica papaya L. preparation, a commercialized functional food. The known compounds were identified as 5-hydroxymethylfurfuraldehyde (1), trans-caffeic acid (2), butyl 4-hydroxybenzoate (butylparaben) (3), lycopene (4), benzyl isothiocyanate (5). Compounds 1 and 3 were reported for the first time from Papaya fruits through this study. The new compound showed a moderate antioxidant activity and a potent hair growth stimulating activity in vitro. 相似文献
106.
It is thought that the therapeutic efficacy of Morus alba L. is determined by its biological compounds. We investigated the chemical differences in the medicinal parts of M. alba by analyzing a total of 57 samples (15 root barks, 11 twigs, 12 fruits, and 19 leaves). Twelve marker compounds, including seven flavonoids, two stilbenoids, two phenolic acids, and a coumarin, were quantitatively analyzed using a high-performance liquid chromatography-diode array detector and chemometric analyses (principal component and heatmap analysis). The results demonstrated that the levels and compositions of the marker compounds varied in each medicinal part. The leaves contained higher levels of six compounds, the root barks contained higher levels of four compounds, and the twigs contained higher levels of two compounds. The results of chemometric analysis showed clustering of the samples according to the medicinal part, with the marker compounds strongly associated with each part: mulberroside A, taxifolin, kuwanon G, and morusin for the root barks; 4-hydroxycinnamic acid and oxyresveratrol for the twigs and skimmin; chlorogenic acid, rutin, isoquercitrin, astragalin, and quercitrin for the leaves. Our approach plays a fundamental role in the quality evaluation and further understanding of biological actions of herbal medicines derived from various medicinal plant parts. 相似文献
107.
108.
研究了Ｃ６０分别在有机玻璃（ＰＭＭＡ）和正己烷中的吸收光谱，发现Ｃ６０在有机玻璃中的吸收峰同在正己烷中相互对应，同时前者的吸收峰相对于后者峰宽变大，峰位产生红移，分析了产生这种现象的原因。 相似文献
109.
乳状液膜法提取Ｌ－谷氨酸的研究徐占林（四平师范学院化学系四平１３６０００）严忠张河哲（东北师范大学化学系长春１３００２４）关键词Ｌ－谷氨酸乳状液膜载体萃取中图分类号Ｏ６２３．７３６氨基酸作为重要的生化产品，广泛应用于食品、饲料、医药、化工等许多领域，... 相似文献
110.
（η^2—C60）[Pt（PPh3）2]8的合成与表征 总被引：6，自引：2，他引：6
C60是高度共轭的宠状结构碳素体．分子结构中六元环间的共价碳碳双键是富电子区，其反应性能与烯键类似，以碳碳双键与中心金属形成η2配位化合物．富勒烯η2配合物的合成及性能研究是当前研究热点之一[1~7]．本文在（η2-C60）［Pt（PPh3）2］n（n=1～6）系列研究[7]的基础上制备了（η2－C60）［Pt（PPh3）2］8，并用元素分析、红外光谱和光电子能谱进行鉴定和表征．1实验部分四（三苯基膦）合铂Pt（PPh3）4按文献[8]方法制备；C60纯度为99％；其余试剂均为分析纯．元素分析在ERLA－1106型元素分析仪上进行；光电子能谱在VGESCA… 相似文献