全文获取类型
收费全文 | 6671篇 |
免费 | 789篇 |
国内免费 | 1篇 |
专业分类
7461篇 |
出版年
2021年 | 76篇 |
2019年 | 83篇 |
2018年 | 68篇 |
2017年 | 58篇 |
2016年 | 105篇 |
2015年 | 158篇 |
2014年 | 186篇 |
2013年 | 232篇 |
2012年 | 334篇 |
2011年 | 297篇 |
2010年 | 165篇 |
2009年 | 173篇 |
2008年 | 226篇 |
2007年 | 238篇 |
2006年 | 218篇 |
2005年 | 233篇 |
2004年 | 212篇 |
2003年 | 227篇 |
2002年 | 226篇 |
2001年 | 196篇 |
2000年 | 212篇 |
1999年 | 154篇 |
1998年 | 89篇 |
1997年 | 73篇 |
1996年 | 83篇 |
1995年 | 80篇 |
1994年 | 68篇 |
1993年 | 80篇 |
1992年 | 152篇 |
1991年 | 136篇 |
1990年 | 138篇 |
1989年 | 171篇 |
1988年 | 131篇 |
1987年 | 126篇 |
1986年 | 100篇 |
1985年 | 117篇 |
1984年 | 117篇 |
1983年 | 91篇 |
1982年 | 80篇 |
1981年 | 76篇 |
1980年 | 78篇 |
1979年 | 109篇 |
1978年 | 88篇 |
1977年 | 63篇 |
1976年 | 71篇 |
1975年 | 71篇 |
1974年 | 81篇 |
1973年 | 79篇 |
1972年 | 56篇 |
1971年 | 53篇 |
排序方式: 共有7461条查询结果,搜索用时 15 毫秒
141.
Summary Brush border membrane vesicles were prepared from mussel gills using differential and sucrose density gradient centrifugation. These vesicles contained both the maximal Na+-dependent alanine transport activity found in the gradient and the maximal activities of -glutamyl transpeptidase and alkaline phosphatase. Electron micrographs showed closed vesicles of approximately 0.1–0.5 m diameter. Transport experiments using these vesicles demonstrated a transient 18-fold overshoot in intravesicular alanine concentration in the presence of an inwardly directed Na+ gradient, but not under Na+ equilibrium conditions. A reduced overshoot (10-fold) was seen with an inwardly directed K+ gradient. Further studies revealed a broad cation selectivity, with preference for Na+, which was characteristic of alanine transport but not glucose transport in these membranes. The apparent amino acid specificity of the uptake pathway(s) was similar to that of intact gills and supported the idea of at least four separate pathways for amino acid transport in mussel gill brush border membranes. The apparent Michaelis constant for alanine uptake was approximately 7m, consistent with values forK
t
determined with intact tissue. 相似文献
142.
Martinez-Burnes J Lopez A Wright GM Ireland WP Wadowska DW Dobbin GV 《Histology and histopathology》2003,18(4):1081-1094
Meconium aspiration syndrome has been for many years an important cause of neonatal respiratory distress in newborn babies and sporadically reported in animals. This investigation was designed to study the ultrastructural and morphometric changes in the lungs of neonatal rats following the intratracheal inoculation of meconium. Seven-day-old Fischer-344 rats (n = 24) were randomly allocated in two groups. One group was intratracheally inoculated with saline solution and the second group received homologous meconium. Neonates were euthanatized at 1, 3 and 7 postinoculation days (PID) and lungs were examined by light and electron microscopy. Saline solution did not induce any ultrastructural changes in the lung. In contrast, meconium induced deciliation, recruitment of neutrophils and pulmonary alveolar macrophages to the bronchoalveolar space, intravascular sequestration of neutrophils and aggregation of platelets at PID 1 and 3. Other ultrastructural changes at PID 1 and 3 included interstitial edema and escape of red cells and fibrin into the alveolar space and interstitium. Interstitial edema and sequestration of neutrophils were responsible for the significant increase in thickness of alveolar septa. At PID 7 there was hyperplasia and enlargement of type II pneumocytes as well as interstitial proliferation of mesenchymal cells with intra-alveolar fibrosis. It was concluded that intratracheal inoculation of meconium in neonatal rats induces acute ultrastructural changes followed by a reparative response. 相似文献
143.
144.
An inhibitor and stimulator of CFU-s proliferation can be obtained from haemopoietic tissue containing, respectively, relatively quiescent CFU-s (e.g. normal bone marrow) and proliferating CFU-s (e.g. regenerating bone marrow). Their effects on the proliferative behaviour of steady-state and regenerating marrow CFU-s, which produce colonies 7, 10 and 12 days post-transplantation have been investigated. The results demonstrate changing sensitivities of CFU-s to inhibitor and stimulator as they progress through a developmental age structure, 'Older' CFU-s (producing early spleen colonies) are more sensitive to stimulator, 'Younger' CFU-s (producing late spleen colonies) are more sensitive to inhibitor. 相似文献
145.
Three cases of adenocarcinoma of the stomach, two in situ and one superficially invasive, and one of superficially invasive squamous-cell carcinoma of the esophagus are presented to illustrate the problems encountered in the diagnosis of early lesions of the upper gastrointestinal (GI) tract and the contribution that cytodiagnosis can make. The symptomology and roentgenographic findings in these cases were largely nonspecific. While endoscopic biopsies were repeatedly negative in three of the four cases, endoscopic brushing cytology consistently indicated the presence of a malignancy. Surgery was finally performed on the basis of the cytologic findings, confirming the presence of early malignancy. The cytologic findings, with histologic correlations, are presented in an effort to define some specific criteria for the diagnosis of early malignancy of the upper GI tract. 相似文献
146.
147.
Martha S. Petrovick Frances E. Nargi Theresa Towle Kristine Hogan Marie Bohane Deborah J. Wright Thomas H. MacRae Malcolm Potts Richard F. Helm 《Biotechnology and bioengineering》2010,106(3):474-481
The unique properties of mammalian cells make them valuable for a variety of applications in medicine, industry, and diagnostics. However, the utility of such cells is restricted due to the difficulty in storing them non‐frozen for an extended time and still maintaining their stability and responsiveness. In order to extend the active life span of a mammalian biosensor cell line at room and refrigerated temperatures, we have over expressed genes that are reported to provide protection from apoptosis, stress, or oxidation. We demonstrated that over expression of genes from the extremophile, Artemia franciscana, as well as GADD45β, extends room‐temperature storage of fully active cells 3.5‐fold, while over production of several anti‐apoptotic proteins extended 4°C storage 2‐ to 3‐fold. Methodologies like these that improve the stability of mammalian‐cell‐based technologies in the absence of freezers may enable widespread use of these tools in applications that have been considered impractical based solely on limited storage characteristics. Biotechnol. Bioeng. 2010; 106: 474–481. © 2010 Wiley Periodicals, Inc. 相似文献
148.
149.
150.
Philippa A. West Natacha Protopopoff Alexandra Wright Zuhura Kivaju Robinson Tigererwa Franklin W. Mosha William Kisinza Mark Rowland Immo Kleinschmidt 《PLoS medicine》2014,11(4)