全文获取类型
收费全文 | 807篇 |
免费 | 43篇 |
国内免费 | 3篇 |
专业分类
耳鼻咽喉 | 3篇 |
儿科学 | 34篇 |
妇产科学 | 20篇 |
基础医学 | 113篇 |
口腔科学 | 52篇 |
临床医学 | 59篇 |
内科学 | 175篇 |
皮肤病学 | 31篇 |
神经病学 | 31篇 |
特种医学 | 29篇 |
外科学 | 71篇 |
综合类 | 12篇 |
一般理论 | 1篇 |
预防医学 | 55篇 |
眼科学 | 51篇 |
药学 | 62篇 |
中国医学 | 5篇 |
肿瘤学 | 49篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 22篇 |
2021年 | 43篇 |
2020年 | 24篇 |
2019年 | 28篇 |
2018年 | 38篇 |
2017年 | 28篇 |
2016年 | 31篇 |
2015年 | 29篇 |
2014年 | 40篇 |
2013年 | 48篇 |
2012年 | 86篇 |
2011年 | 86篇 |
2010年 | 50篇 |
2009年 | 35篇 |
2008年 | 41篇 |
2007年 | 62篇 |
2006年 | 31篇 |
2005年 | 30篇 |
2004年 | 35篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 1篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1985年 | 1篇 |
1975年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有853条查询结果,搜索用时 15 毫秒
1.
2.
Fangli Chen Margaret Barkett Kavitha T. Ram Adrian Quintanilla Iswar K. Hariharan 《Proceedings of the National Academy of Sciences of the United States of America》1997,94(23):12485-12490
The activity of Ras family proteins is modulated in vivo by the function of GTPase activating proteins, which increase their intrinsic rate of GTP hydrolysis. We have isolated cDNAs encoding a GAP for the Drosophila Rap1 GTPase. Drosophila Rapgap1 encodes an 850-amino acid protein with a central region that displays substantial sequence similarity to human RapGAP. This domain, when expressed in Escherichia coli, potently stimulates Rap1 GTPase activity in vitro. Unlike Rap1, which is ubiquitously expressed, Rapgap1 expression is highly restricted. Rapgap1 is expressed at high levels in the developing photoreceptor cells and in the optic lobe. Rapgap1 mRNA is also localized in the pole plasm in an oskar-dependent manner. Although mutations that completely abolish Rapgap1 function display no obvious phenotypic abnormalities, overexpression of Rapgap1 induces a rough eye phenotype that is exacerbated by reducing Rap1 gene dosage. Thus, Rapgap1 can function as a negative regulator of Rap1-mediated signaling in vivo. 相似文献
3.
Tuberculosis (TB) is a common infection affecting patients with human immunodeficiency virus (HIV) and diabetes mellitus (DM). With the increasing incidence of HIV infection and DM in a developing country like India, TB is definitely on the rise. In a given population, one expects to see these three diseases in varying combinations, such as HIV and TB, DM and TB, HIV and DM with TB. In such combinations TB may lack the characteristic clinical and histological picture due to the associated depressed cell-mediated immunity seen in both diseases and TB may have an unusual clinical presentation and cytology picture. In this retrospective study of 36 months, from January 1997 to December 1999, 109 cases diagnosed cytologically as tuberculous lymphadenitis and tested for HIV infection and investigated as well for DM were selected. Forty-six (42%) were nondiabetic HIV patients, 13 (12%) were non-HIV DM patients, and 50 (46%) had TB without HIV infection or DM. The coexistence of both HIV and DM was not noted. The cytomorphological characteristics supplemented by culture studies of each of these three groups were compared in detail and based on these four cytological patterns, Pattern 1, Pattern 2, Pattern 3, and Pattern 4 emerged and were characterized. This study highlights the usefulness of cytomorphology of the lymph nodes to characterize the cytopathological profile of TB in both HIV and DM, which have many clinical and immunological similarities, and indirectly postulate the extent of immune suppression and evolve effective strategies in the management of coexisting diseases. Such a comparative study has not been carried out in the past. 相似文献
4.
Decellularized vascular matrices are used as scaffolds in cardiovascular tissue engineering because they retain their natural biological composition and three-dimensional (3-D) architecture suitable for cell adhesion and proliferation. However, cell infiltration and subsequent repopulation of these scaffolds was shown to be unsatisfactory due to their dense collagen and elastic fiber networks. In an attempt to create more porous structures for cell repopulation, we selectively removed matrix components from decellularized porcine aorta to obtain two types of scaffolds, namely elastin and collagen scaffolds. Histology and scanning electron microscopy examination of the two scaffolds revealed a well-oriented porous decellularized structure that maintained natural architecture of the aorta. Quantitative DNA analysis confirmed that both scaffolds were completely decellularized. Stress-strain analysis demonstrated adequate mechanical properties for both elastin and collagen scaffolds. In vitro enzyme digestion of the scaffolds suggested that they were highly biodegradable. Furthermore, the biodegradability of collagen scaffolds could be controlled by crosslinking with carbodiimides. Cell culture studies showed that fibroblasts adhered to and proliferated on the scaffold surfaces with excellent cell viability. Fibroblasts infiltrated about 120 microm into elastin scaffolds and about 40 microm into collagen scaffolds after 4 weeks of rotary cell culture. These results indicated that our novel aortic elastin and collagen matrices have the potential to serve as scaffolds for cardiovascular tissue engineering. 相似文献
5.
6.
A silencing pathway to induce H3-K9 and H4-K20 trimethylation at constitutive heterochromatin 总被引:31,自引:1,他引:31 下载免费PDF全文
Schotta G Lachner M Sarma K Ebert A Sengupta R Reuter G Reinberg D Jenuwein T 《Genes & development》2004,18(11):1251-1262
Histone lysine methylation is a central modification to mark functionally distinct chromatin regions. In particular, H3-K9 trimethylation has emerged as a hallmark of pericentric heterochromatin in mammals. Here we show that H4-K20 trimethylation is also focally enriched at pericentric heterochromatin. Intriguingly, H3-K9 trimethylation by the Suv39h HMTases is required for the induction of H4-K20 trimethylation, although the H4 Lys 20 position is not an intrinsic substrate for these enzymes. By using a candidate approach, we identified Suv4-20h1 and Suv4-20h2 as two novel SET domain HMTases that localize to pericentric heterochromatin and specifically act as nucleosomal H4-K20 trimethylating enzymes. Interaction of the Suv4-20h enzymes with HP1 isoforms suggests a sequential mechanism to establish H3-K9 and H4-K20 trimethylation at pericentric heterochromatin. Heterochromatic H4-K20 trimethylation is evolutionarily conserved, and in Drosophila, the Suv4-20 homolog is a novel PEV modifier to regulate position-effect variegation. Together, our data indicate a function for H4-K20 trimethylation in gene silencing and further suggest H3-K9 and H4-K20 trimethylation as important components of a repressive pathway that can index pericentric heterochromatin. 相似文献
7.
Adenosine Deaminase (ADA) levels were estimated in cord blood of 30 neonates born with birth weight less than or equal to 2.5 kg and 30 neonates born with birth weight greater than 2.5 kg. The mean ADA levels in low birth weight (LBW) group was found to be 6.94 U/L and in normal birth weight group the mean ADA levels were 14.37 U/L which was statistically significant. Therefore ADA may be useful in assessing CMI status in low birth weight infants. 相似文献
8.
Michael A Repka Kavitha Gutta Suneela Prodduturi Manish Munjal Steven P Stodghill 《European journal of pharmaceutics and biopharmaceutics》2005,59(1):189-196
Hot-melt extrusion technology was used to produce thin films containing a model drug, lidocaine, and the cellulosic polymers hydroxypropyl cellulose (HPC) and hydroxypropyl methyl cellulose (HPMC). Two film formulations were extruded and compared, one containing only HPC and the other containing HPC:HPMC (80:20). Thermal analysis of the films using differential scanning calorimetry (DSC) suggested that the drug existed in the amorphous condition, which was confirmed by wide angle X-ray diffractometry. Sustained release of the drug was observed from both of the polymer matrices. Dissolution profiles suggested that HPMC retarded the drug release from HPC:HPMC (80:20) films. However, the mechanism of drug release from both of the films was predominantly diffusion of the drug through the polymer matrices. Incorporation of HPMC also increased both adhesive strength and work of adhesion as compared to the HPC-only films. 相似文献
9.
The management of congenital heart disease (CHD) remains a significant challenge in developing regions. Since 2006, China
California Heart Watch has provided cardiac services in China’s Yunnan province. Our Grants for Kids program aims to diagnose
and fund surgical and nonsurgical treatments for underprivileged children with congenitally malformed hearts. This report
analyzes our patient outcomes. From 2007 to 2010, 36 children with CHD underwent either surgical or percutaneous procedures
at local Chinese medical centers, and 94% of our patients could be contacted for follow-up assessment. The mortality and complication
rates of our patient population compare favorably with international data. Our study provides a model through which networking
with local hospitals and regional cardiac centers can be an effective way to assist developing areas in providing cardiac
care to rural underserved populations. 相似文献
10.
Hong Chee Chew Arjun Iyer Mark Connellan Sarah Scheuer Jeanette Villanueva Ling Gao Mark Hicks Michelle Harkness Claudio Soto Andrew Dinale Priya Nair Alasdair Watson Emily Granger Paul Jansz Kavitha Muthiah Andrew Jabbour Eugene Kotlyar Anne Keogh Kumud Dhital 《Journal of the American College of Cardiology》2019,73(12):1447-1459