全文获取类型
收费全文 | 1907篇 |
免费 | 27篇 |
国内免费 | 52篇 |
专业分类
系统科学 | 43篇 |
丛书文集 | 31篇 |
教育与普及 | 35篇 |
理论与方法论 | 98篇 |
现状及发展 | 30篇 |
研究方法 | 82篇 |
综合类 | 1667篇 |
出版年
2023年 | 24篇 |
2022年 | 57篇 |
2021年 | 63篇 |
2020年 | 16篇 |
2019年 | 22篇 |
2018年 | 31篇 |
2017年 | 67篇 |
2016年 | 71篇 |
2015年 | 72篇 |
2014年 | 30篇 |
2013年 | 26篇 |
2012年 | 74篇 |
2011年 | 98篇 |
2010年 | 90篇 |
2009年 | 31篇 |
2008年 | 84篇 |
2007年 | 87篇 |
2006年 | 91篇 |
2005年 | 103篇 |
2004年 | 109篇 |
2003年 | 184篇 |
2002年 | 67篇 |
2001年 | 135篇 |
2000年 | 108篇 |
1999年 | 67篇 |
1998年 | 27篇 |
1997年 | 16篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1960年 | 14篇 |
1959年 | 5篇 |
1958年 | 3篇 |
排序方式: 共有1986条查询结果,搜索用时 296 毫秒
111.
BMP signaling inhibits intestinal stem cell self-renewal through suppression of Wnt-beta-catenin signaling 总被引:21,自引:0,他引:21
He XC Zhang J Tong WG Tawfik O Ross J Scoville DH Tian Q Zeng X He X Wiedemann LM Mishina Y Li L 《Nature genetics》2004,36(10):1117-1121
In humans, mutations in BMPR1A, SMAD4 and PTEN are responsible for juvenile polyposis syndrome, juvenile intestinal polyposis and Cowden disease, respectively. The development of polyposis is a common feature of these diseases, suggesting that there is an association between BMP and PTEN pathways. The mechanistic link between BMP and PTEN pathways and the related etiology of juvenile polyposis is unresolved. Here we show that conditional inactivation of Bmpr1a in mice disturbs homeostasis of intestinal epithelial regeneration with an expansion of the stem and progenitor cell populations, eventually leading to intestinal polyposis resembling human juvenile polyposis syndrome. We show that BMP signaling suppresses Wnt signaling to ensure a balanced control of stem cell self-renewal. Mechanistically, PTEN, through phosphatidylinosital-3 kinase-Akt, mediates the convergence of the BMP and Wnt pathways on control of beta-catenin. Thus, BMP signaling may control the duplication of intestinal stem cells, thereby preventing crypt fission and the subsequent increase in crypt number. 相似文献
112.
Davila S Furu L Gharavi AG Tian X Onoe T Qian Q Li A Cai Y Kamath PS King BF Azurmendi PJ Tahvanainen P Kääriäinen H Höckerstedt K Devuyst O Pirson Y Martin RS Lifton RP Tahvanainen E Torres VE Somlo S 《Nature genetics》2004,36(6):575-577
Mutations in PRKCSH, encoding the beta-subunit of glucosidase II, an N-linked glycan-processing enzyme in the endoplasmic reticulum (ER), cause autosomal dominant polycystic liver disease. We found that mutations in SEC63, encoding a component of the protein translocation machinery in the ER, also cause this disease. These findings are suggestive of a role for cotranslational protein-processing pathways in maintaining epithelial luminal structure and implicate noncilial ER proteins in human polycystic disease. 相似文献
113.
114.
The new Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite image offers a large choice of opportunities for operational applications. The 1-km Advanced Very High Resolution Radiometer (AVHRR) image is not suitable for retrieval of field level parameter and Landsat data are not frequent enough for monitoring changes in crop parameters during the critical crop growth periods.A methodology to map areas of paddy fields using MODIS,geographic information system (GIS) and global position system (GPS) is introduced in this paper. Training samples are selected and located with the help of GPS to provide maximal accuracy.A concept of assessing areas of potential cultivation of rice is suggested by means of GIS integration. By integration of MODIS with GIS and GPS technologies the actual areas of rice fields in 2002 have been mapped. The classification accuracy was 95.7% percent compared with the statistical data of the Agricultural Bureau of Zhejiang Province. 相似文献
115.
Early association of electrocardiogram alteration with infarct size and cardiac function after myocardial infarction 总被引:7,自引:0,他引:7
OBJECTIVE: Myocardial infarction (MI) is the main cause of heart failure, but the relationship between the extent of MI and cardiac function has not been clearly determined. The present study was undertaken to investigate early changes in the electrocardiogram associated with infarct size and cardiac function after MI. METHODS: MI was induced by ligating the left anterior descending coronary artery in rats. Electrocardiograms, echocardiographs and hemodynamic parameters were assessed and myocardial infarct size was measured from mid-transverse sections stained with Masson's trichrome. RESULTS: The sum of pathological Q wave amplitudes was strongly correlated with myocardial infarct size (r = 0.920, P < 0.0001), left ventricular ejection fraction (r = -0.868, P < 0.0001) and left ventricular end diastolic pressure (r = 0.835, P < 0.0004). Furthermore, there was close relationship between MI size and cardiac function as assessed by left ventricular ejection fraction (r = -0.913, P < 0.0001) and left ventricular end diastolic pressure (r = 0.893, P < 0.0001). CONCLUSION: The sum of pathological Q wave amplitudes after MI can be used to estimate the extent of MI as well as cardiac function. 相似文献
116.
探讨针刺穴位,究竟对大脑皮层的机能状态发生什么影响,是研究针麻原理的课题之一。大脑皮层的诱发电位,在一定程度上,反映了感觉冲动的传入过程以及皮层的机能状态。近年来,针刺对大脑皮层诱发电位的影响,在动物上进行试验,已有许多报道,但在人体上进行试验的报道不多。现在,我们试图以人的头顶诱发电位(Vertex Potential)作为 相似文献
117.
西安交通大学无线电元件与材料教研室中放科研组 《西安交通大学学报》1974,(1)
本文介绍30MHZ中放电路薄厚膜集成化的试制,在试制中所采用的集成化的结构形式,各种薄厚膜元件和基片所使用的材料及其某些性能指标。另外还着重介绍了某些元件集成化后所带来的问题和集成化后调试过程中所遇到的寄生反馈等等问题。最后也指出了今后有待工作的方向。 相似文献
118.
Frustrated systems are ubiquitous, and they are interesting because their behaviour is difficult to predict; frustration can lead to macroscopic degeneracies and qualitatively new states of matter. Magnetic systems offer good examples in the form of spin lattices, where all interactions between spins cannot be simultaneously satisfied. Here we report how unusual composite spin degrees of freedom can emerge from frustrated magnetic interactions in the cubic spinel ZnCr(2)O(4). Upon cooling, groups of six spins self-organize into weakly interacting antiferromagnetic loops, whose directors -- the unique direction along which the spins are aligned, parallel or antiparallel -- govern all low-temperature dynamics. The experimental evidence comes from a measurement of the magnetic form factor by inelastic neutron scattering; the data show that neutrons scatter from hexagonal spin clusters rather than individual spins. The hexagon directors are, to a first approximation, decoupled from each other, and hence their reorientations embody the long-sought local zero energy modes for the pyrochlore lattice. 相似文献
119.
120.
Bird AW Yu DY Pray-Grant MG Qiu Q Harmon KE Megee PC Grant PA Smith MM Christman MF 《Nature》2002,419(6905):411-415