全文获取类型
收费全文 | 7870篇 |
免费 | 843篇 |
专业分类
8713篇 |
出版年
2022年 | 59篇 |
2021年 | 98篇 |
2020年 | 73篇 |
2019年 | 66篇 |
2018年 | 117篇 |
2017年 | 101篇 |
2016年 | 159篇 |
2015年 | 284篇 |
2014年 | 294篇 |
2013年 | 382篇 |
2012年 | 507篇 |
2011年 | 424篇 |
2010年 | 301篇 |
2009年 | 279篇 |
2008年 | 374篇 |
2007年 | 342篇 |
2006年 | 296篇 |
2005年 | 294篇 |
2004年 | 270篇 |
2003年 | 270篇 |
2002年 | 294篇 |
2001年 | 196篇 |
2000年 | 219篇 |
1999年 | 177篇 |
1998年 | 97篇 |
1997年 | 98篇 |
1996年 | 80篇 |
1995年 | 78篇 |
1994年 | 58篇 |
1993年 | 70篇 |
1992年 | 141篇 |
1991年 | 143篇 |
1990年 | 148篇 |
1989年 | 134篇 |
1988年 | 110篇 |
1987年 | 128篇 |
1986年 | 115篇 |
1985年 | 102篇 |
1984年 | 104篇 |
1983年 | 74篇 |
1982年 | 58篇 |
1981年 | 68篇 |
1980年 | 46篇 |
1979年 | 78篇 |
1978年 | 46篇 |
1977年 | 65篇 |
1975年 | 53篇 |
1974年 | 49篇 |
1973年 | 63篇 |
1971年 | 49篇 |
排序方式: 共有8713条查询结果,搜索用时 0 毫秒
1.
In this work, incorporation of plasmid DNA, pre-complexed with PEI, into polyelectrolyte multilayers has been studied to further develop platforms for local gene delivery. Polyplex embedding in synthetic and naturally degradable architectures was efficient for transfection of human hepato-cellular carcinoma cells. 相似文献
2.
3.
Thorsten Thye Genevieve Scarisbrick Edmund N. L. Browne Margaret Amanua Chinbuah John Gyapong Ivy Osei Ellis Owusu-Dabo Stefan Niemann Sabine Rüsch-Gerdes Christian G. Meyer Rolf D. Horstmann 《PloS one》2009,4(7)
The gene of Cytotoxic T Lymphocyte-associated Antigen 4 (CTLA4), a negative regulator of T lymphocytes, contains a single-nucleotide polymorphism (SNP) at position +6230A->G (ct60A->G), which has been found associated with several autoimmune diseases and appears to reduce T-cell inhibitory activity. In Ghana, West Africa, we compared the frequencies of CTLA4 +6230 A/G and 6 haplotype-tagging SNPs in 2010 smear-positive, HIV-negative patients with pulmonary tuberculosis (TB) and 2346 controls matched for age, gender and ethnicity. We found no difference in allele frequencies between cases and controls. However, +6230A and a distinct CTLA4 haplotype and a diplotype comprising the +6230A allele were significantly less frequent among cases with large opacities in chest radiographs compared to those with small ones (Pcorrected [cor] = 0.002, Pcor = 0.00045, P = 0.0005, respectively). This finding suggests that an increased T-cell activity associated with the CTLA4 +6230G allele contributes to pathology rather than to protection in pulmonary TB. 相似文献
4.
A total dosage up to 1 mg PGF2a as i.v. infusions of 10–40 μg/min. was investigated on patients with arrhythmias of several kinds. We found therapeutic effects in 5 of 6 patients with constant extrasystoles and in one patient with digitalis - induced partial AV-block respectively. In 3 of 4 patients with acute tachyarrhythmias the results were not convincing, probably due to a dosage not high enough. An increase of the diastolic stimulation threshold usually seen with other antiarrhythmics was not to be observed in 3 patients. The mechanism of action of PGF2a has not yet been clarified. 相似文献
5.
With enzyme histochemical methods, the distribution and the activities of various oxidative and hydrolytic enzymes in the apocrine glands of the general body surface of the domestic cat were investigated. The results obtained support the view that these glands are clearly active in function. On the whole, however, the relatively weak enzyme activities in the secretory portion of the glands point to only unimportant secretion production rates. 相似文献
6.
Laura Cernat Cristina Blaj Rene Jackstadt Lydia Brandl Jutta Engel Heiko Hermeking Andreas Jung Thomas Kirchner David Horst 《PloS one》2014,9(8)
Colonic crypts are stereotypical structures with distinct stem cell, proliferating, and differentiating compartments. Colorectal cancers derive from colonic crypt epithelia but, in contrast, form morphologically disarrayed glands. In this study, we investigated to which extent colorectal cancers phenocopy colonic crypt architecture and thus preserve structural organization of the normal intestinal epithelium. A subset of colon cancers showed crypt-like compartments with high WNT activity and nuclear β-Catenin at the leading tumor edge, adjacent proliferation, and enhanced Cytokeratin 20 expression in most differentiated tumor epithelia of the tumor center. This architecture strongly depended on growth conditions, and was fully reproducible in mouse xenografts of cultured and primary colon cancer cells. Full crypt-like organization was associated with low tumor grade and was an independent prognostic marker of better survival in a collection of 221 colorectal cancers. Our findings suggest that full activation of preserved intestinal morphogenetic programs in colon cancer requires in vivo growth environments. Furthermore, crypt-like architecture was linked with less aggressive tumor biology, and may be useful to improve current colon cancer grading schemes. 相似文献
7.
C Gerdemann C Eicken A Magrini H E Meyer A Rompel F Spener B Krebs 《Biochimica et biophysica acta》2001,1548(1):94-105
The amino acid sequences of two isozymes of catechol oxidase from sweet potatoes (Ipomoea batatas) were determined by Edman degradation of BrCN cleavage fragments of the native protein and by sequencing of amplified cDNA fragments. Sequence alignment and phylogenetic analysis of plant catechol oxidases revealed about 80% equidistance between the two I. batatas catechol oxidases and approximately 40--60% to catechol oxidases of other plants. When H(2)O(2) was applied as substrate the 39 kDa isozyme, but not the 40 kDa isozyme, showed catalase-like activity. The structure of the 40 kDa isozyme was modeled on the basis of the published crystal structure of the 39 kDa isozyme [T. Klabunde et al., Nat. Struct. Biol. 5 (1998) 1084]. The active site model closely resembled that of the 39 kDa isozyme determined by crystallography, except for a mutation of Thr243 (40 kDa isozyme) to Ile241 (39 kDa isozyme) close to the dimetal center. This residue difference affects the orientation of the Glu238/236 residue, which is thought to be responsible for the catalase-like activity of the 39 kDa isozyme for which a catalytic mechanism is proposed. 相似文献
8.
9.
10.
Se-Chan Kim Alexander Ghanem Heidi Stapel Klaus Tiemann Pascal Knuefermann Andreas Hoeft Rainer Meyer Christian Grohé Anne A Knowlton Georg Baumgarten 《BMC physiology》2007,7(1):5