全文获取类型
收费全文 | 23868篇 |
免费 | 549篇 |
国内免费 | 749篇 |
专业分类
系统科学 | 727篇 |
丛书文集 | 459篇 |
教育与普及 | 195篇 |
理论与方法论 | 128篇 |
现状及发展 | 4429篇 |
研究方法 | 562篇 |
综合类 | 18395篇 |
自然研究 | 271篇 |
出版年
2022年 | 227篇 |
2021年 | 248篇 |
2020年 | 213篇 |
2018年 | 210篇 |
2017年 | 227篇 |
2016年 | 296篇 |
2015年 | 423篇 |
2014年 | 637篇 |
2013年 | 738篇 |
2012年 | 889篇 |
2011年 | 1377篇 |
2010年 | 880篇 |
2009年 | 991篇 |
2008年 | 1128篇 |
2007年 | 1131篇 |
2006年 | 1043篇 |
2005年 | 966篇 |
2004年 | 838篇 |
2003年 | 695篇 |
2002年 | 802篇 |
2001年 | 816篇 |
2000年 | 698篇 |
1999年 | 497篇 |
1998年 | 180篇 |
1996年 | 179篇 |
1992年 | 249篇 |
1991年 | 196篇 |
1990年 | 206篇 |
1989年 | 212篇 |
1988年 | 195篇 |
1987年 | 203篇 |
1986年 | 182篇 |
1985年 | 253篇 |
1984年 | 181篇 |
1979年 | 331篇 |
1978年 | 256篇 |
1977年 | 240篇 |
1976年 | 225篇 |
1975年 | 238篇 |
1974年 | 305篇 |
1973年 | 279篇 |
1972年 | 236篇 |
1971年 | 337篇 |
1970年 | 474篇 |
1969年 | 327篇 |
1968年 | 313篇 |
1967年 | 319篇 |
1966年 | 349篇 |
1965年 | 223篇 |
1958年 | 209篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
61.
62.
通过对师范院校体育教育专业篮球教学目标、教学内容、教学模式、课的结构及对学生的学业成绩评价进行分析和思考 ,提出了当今篮球教学中存在的问题及其解决方法。 相似文献
63.
李惠 《厦门理工学院学报》2002,10(1):48-51
本文从应交增值税的核算角度探讨增值税的征收管理 ,认为应该把销项税额与进项税额的核算基础由现行的权责发生制改为收付实现制 ,从而有效控制偷、逃税现象 ,同时促进增值税税收征管的改革 ,使增值税征收管理的方式、手段更趋严密、科学。又从购进固定资产所支付的进项税额的核算角度探讨增值税制由生产型增值税转为消费型增值税 ,认为这种转型有利于提高企业产品的市场竞争力及西部大开发战略的实施等 相似文献
64.
65.
Obese postmenopausal female volunteers were given timed daily oral dosages of bromocriptine, and tested for reduction of body fat stores. This dopamine agonist has been shown to reset circadian rhythms that are altered in obese animals and to reduce body fat levels in several animal models. The participants were instructed not to alter their existing exercise and eating behavior during treatment. Skinfold measurements were taken on 33 subjects as indices of body fat. The measurements (e.g., suprailiac) were reduced after six weeks by about 25%, which represents a reduction of 11.7% of the total body fat. These dramatic decreases in body fat, which are equivalent to that produced by severe caloric restriction, were accompanied by more modest reductions of body weight (2.5%), indicating a possible conservation of protein that is usually lost as a consequence of such caloric restriction. The effects of bromocriptine treatment on body fat and hyperglycemia were also examined in non-insulin dependent diabetics being treated with oral hypoglycemics (7 subjects) or insulin (7 subjects). Total body fat was reduced by 10.7% and 5.1% in diabetics on oral hypoglycemics and insulin, respectively, without any significant reductions in body weight. Hyperglycemia was reduced in most of the 15 diabetic subjects treated leading to euglycemia and even cessation of hypoglycemic drugs in 3 of the 7 subjects during 4-8 weeks of bromocriptine treatment. These findings support the hypothesis that obesity and type II diabetes may be treated effectively with bromocriptine when administered at the proper times and dosages. 相似文献
66.
运用电磁理论与流体静压力原理,导出了电弧自身的电磁向心压缩力以及电弧对熔池冲力的解析式。又运用辐射传热原理,导出了单电极电弧对熔池与炉衬辐射传热的解析式。解析式揭示出电弧自身电磁向心压缩力、电弧对熔池冲力,单电极电弧对熔池以及对炉衬辐射传热的规律。 相似文献
67.
Short alanine peptides, containing 16 or 17 residues, appear to form alpha-helices in aqueous solution. But the main spectroscopic analyses used on helical peptides (circular dichroism and nuclear magnetic resonance) cannot distinguish between an alpha-helix (in which the ith residue is hydrogen-bonded to residue i + 4; ref. 9) and the next most common peptide helix, the 3(10)-helix10 (i-->i + 3 hydrogen-bonding). To address this problem we have designed single and doubly spin-labelled analogues of alanine-based peptides in which the nitroxide spin label forms an unbranched side chain extending from the sulphur atom of a cysteine residue. Here we report the circular dichroism, Fourier-transform infrared and electron-spin resonance spectra of these peptides under helix-forming conditions. The infrared absorbance gives an amide I' band with a frequency that is substantially different from that observed for alpha-helices. The electron-spin resonance spectra of doubly labelled helices show that the ranking of distances between side chains, around a single turn (residues 4-8), is inconsistent with an alpha-helical structure. Our experiments suggest that the more likely peptide geometry is a 3(10)-helix. 相似文献
68.
王晖 《青海师范大学学报(自然科学版)》1994,(3):60-64
本文对科技文献的作用,特征进行了分析。探讨了科技文献检索途径、方法及质量对科学研究活动的影响。 相似文献
69.
70.
K K Leong K M Yu W B Lee 《厦门大学学报(自然科学版)》2002,(Z1)
Product data management (PDM) has been accepted as an important tool for the manufacturing industries. In recent years, more and mor e researches have been conducted in the development of PDM. Their research area s include system design, integration of object-oriented technology, data distri bution, collaborative and distributed manufacturing working environment, secur ity, and web-based integration. However, there are limitations on their rese arches. In particular, they cannot cater for PDM in dis... 相似文献