全文获取类型
收费全文 | 13576篇 |
免费 | 564篇 |
国内免费 | 1052篇 |
专业分类
系统科学 | 888篇 |
丛书文集 | 330篇 |
教育与普及 | 128篇 |
理论与方法论 | 54篇 |
现状及发展 | 87篇 |
研究方法 | 23篇 |
综合类 | 13682篇 |
出版年
2024年 | 50篇 |
2023年 | 107篇 |
2022年 | 215篇 |
2021年 | 264篇 |
2020年 | 204篇 |
2019年 | 175篇 |
2018年 | 180篇 |
2017年 | 209篇 |
2016年 | 277篇 |
2015年 | 474篇 |
2014年 | 620篇 |
2013年 | 757篇 |
2012年 | 856篇 |
2011年 | 985篇 |
2010年 | 994篇 |
2009年 | 994篇 |
2008年 | 1123篇 |
2007年 | 1075篇 |
2006年 | 977篇 |
2005年 | 883篇 |
2004年 | 633篇 |
2003年 | 449篇 |
2002年 | 579篇 |
2001年 | 531篇 |
2000年 | 442篇 |
1999年 | 296篇 |
1998年 | 125篇 |
1997年 | 137篇 |
1996年 | 97篇 |
1995年 | 103篇 |
1994年 | 78篇 |
1993年 | 56篇 |
1992年 | 50篇 |
1991年 | 45篇 |
1990年 | 36篇 |
1989年 | 39篇 |
1988年 | 37篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1972年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
This paper presents a novel Web Service based distributed collaborative CAD system employing feature as its collaborative design element and uses XML to define feature operations and communication protocol between the server and the client. To reduce network load and increase response ability of the system, the feature information is updated incrementally on the client. The system supports collaborative designing on heterogeneous platforms. Its framework and communication protocols are analyzed in detail. The experimental results from the developed prototype system showed that it can effectively support collaborative design under the distributed environment. 相似文献
902.
MRS study on lentiform nucleus in idiopathic Parkinson‘s disease with unilateral symptoms 总被引:5,自引:0,他引:5
OBJECTIVE: To investigate changes in magnetic resonance spectroscopy (MRS) of lentiform nucleus during the early stage of Parkinson's disease. METHODS: Twenty-five patients with idiopathic Parkinson disease with unilateral symptoms (IPDUS) and 25 healthy volunteers were enrolled in this study. MRS of the lentiform nucleus in each patient was taken and then concentrations of N-acetylaspartate (NAA), Creatine (Cr) and Choline (Cho) were calculated. RESULTS: Compared to that in the control, NAA/ (Cho+Cr) was significantly lower in the lentiform nucleus contralateral to symptoms and even that in the ipsilateral side in IPDUS patients (all P<0.05); while there was no difference between the two sides in the healthy volunteer (P>0.05). The ratio of NAA/(Cho+Cr) ipsilateral to the sympatomatic side of the patient was also lower than that of the control (P<0.05). CONCLUSIONS: There might be some changes with MRS on the lentiform nucleus during the early stage of idiopathic Parkinson's disease with unilateral symptom. MRS may be one of the reliable methods for early or even sub-clinical diagnosis. 相似文献
903.
略论把流通业提升为先导产业(一) 总被引:2,自引:0,他引:2
流通业的兴起具有深刻的经济渊源。把流通业提升为先导产业是社会主义市场经济体制初步确立、“生产相对过剩”和加入WTO新形势的必然要求。将这一要求转化成政策并付诸实践,需要我们大胆创新,确立相应的软环境和硬环境。 相似文献
904.
A semantic retrieval method based on the fuzzy reasoning 总被引:1,自引:0,他引:1
This paper gives a semantic fuzzy retrieval method of multimedia object, discusses the principle of fuzzy semantic retrieval
technique, presents a fuzzy reasoning mechanism based on the knowledge base, and designs the relevant reasoning algorithms.
Researchful results have innovative significance.
Foundation item: Supported by the Natural Science Foundation of Hubei Province(No. 200J157)
Biography: Cao Jia-heng(1946-), male, Professor, research direction: multimedia software, artificial intelligence. 相似文献
905.
以“休憩、交流、凝聚、升华”为设计原则 ,运用格网控制法等新的设计理念和手法 ,规划设计了河北职业技术师范学院“砺慧园” ,为教职工和学生创设了一个富有现代气息、舒适开敞的休憩、娱乐、学习环境。 相似文献
906.
秩序向量表偶S=[A,B]完全k强的充要条件 总被引:2,自引:0,他引:2
给出秩序向量表偶 S=[A ,B]是二部竞赛图的完全 k强得分表偶的充要条件 ,部分解决了李炯生在“关于图的度序列”中提出的问题。 相似文献
907.
心灵的传承——试论《简爱》对《蝴蝶梦》的影响 总被引:1,自引:0,他引:1
赵敏 《文山师范高等专科学校学报》2001,13(2):26-30,35
本文以新的视角,对欧洲两部著名文学作品《简爱》与《蝴蝶梦》进行了详尽的比较分析,并从人物刻画、结构设置和艺术处理等多方面入手,剖析了作品成功的审美因素,进而透视出了文学遗产复杂微妙的继承关系。 相似文献
908.
The Diels-Alder reaction, which forms a six-membered ring from an alkene (dienophile) and a 1,3-diene, is synthetically very useful for construction of cyclic products with high regio- and stereoselectivity under mild conditions. It has been applied to the synthesis of complex pharmaceutical and biologically active compounds. Although evidence on natural Diels-Alderases has been accumulated in the biosynthesis of secondary metabolites, there has been no report on the structural details of the natural Diels-Alderases. The function and catalytic mechanism of the natural Diels-Alderase are of great interest owing to the diversity of molecular skeletons in natural Diels-Alder adducts. Here we present the 1.70 A resolution crystal structure of the natural Diels-Alderase, fungal macrophomate synthase (MPS), in complex with pyruvate. The active site of the enzyme is large and hydrophobic, contributing amino acid residues that can hydrogen-bond to the substrate 2-pyrone. These data provide information on the catalytic mechanism of MPS, and suggest that the reaction proceeds via a large-scale structural reorganization of the product. 相似文献
909.
910.
对现代性过程的三个重要阶段上的社会学理论形态———工业化社会的社会学、民主社会与转型社会的社会学、现代性遭遇全球化时代的社会学———进行了分析 ,对社会学理论范域的多变形态进行了探讨。这些讨论所包含的蕴意在于 ,“现代”是个人和社会经历巨大裂峡的时代 ,也是个人和社会的共生互构的时代。当代社会学应当有属于自己时代的理论回应。 相似文献