全文获取类型
收费全文 | 621337篇 |
免费 | 63048篇 |
国内免费 | 776篇 |
出版年
2018年 | 6683篇 |
2017年 | 6329篇 |
2016年 | 8599篇 |
2015年 | 10834篇 |
2014年 | 13121篇 |
2013年 | 18050篇 |
2012年 | 21301篇 |
2011年 | 22147篇 |
2010年 | 14962篇 |
2009年 | 13462篇 |
2008年 | 19510篇 |
2007年 | 20166篇 |
2006年 | 19065篇 |
2005年 | 18033篇 |
2004年 | 18201篇 |
2003年 | 17147篇 |
2002年 | 16777篇 |
2001年 | 25808篇 |
2000年 | 25552篇 |
1999年 | 20197篇 |
1998年 | 7300篇 |
1997年 | 7166篇 |
1996年 | 6798篇 |
1995年 | 6425篇 |
1994年 | 6140篇 |
1993年 | 6098篇 |
1992年 | 16571篇 |
1991年 | 16703篇 |
1990年 | 16423篇 |
1989年 | 15938篇 |
1988年 | 14794篇 |
1987年 | 13974篇 |
1986年 | 13200篇 |
1985年 | 13144篇 |
1984年 | 10772篇 |
1983年 | 9221篇 |
1982年 | 6777篇 |
1981年 | 6012篇 |
1980年 | 5721篇 |
1979年 | 10048篇 |
1978年 | 8045篇 |
1977年 | 7224篇 |
1976年 | 6833篇 |
1975年 | 8014篇 |
1974年 | 8780篇 |
1973年 | 8562篇 |
1972年 | 7678篇 |
1971年 | 7159篇 |
1970年 | 6072篇 |
1969年 | 5987篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
Severe aortic valve stenosis (AVS) and mitral valve regurgitation (MVR) often coexist. Although a fully percutaneous treatment for the two conditions, by means of transcatheter aortic valve implantation (TAVI) followed by MitraClip, can be appealing in selected high-risk candidates, critical and strategical reasoning should be applied. In a 3-year period we have developed a single-centre experience of 14 patients who were managed with a staged percutaneous approach to treat severe AVS and MVR. The average interval from TAVI to MitraClip repair was 101 ± 12 days. Success for TAVI was 100% and 92.9% (13/14) for MitraClip. At late follow-up, 3 patients developed MVR 3+. Estimated 1?year survival was 66.5%. Freedom from 1?year endpoint (death, stroke, major bleeding, myocardial infarction, and cardiac re-hospitalisation) was 57.9%.In our view, a fully transcatheter approach for mitro-aortic pathology is feasible and should be performed only as a staged procedure in those patients that remain symptomatic, in spite of successful TAVI. It should be emphasised that although the periprocedural success rate is satisfactory, follow-up mortality and re-hospitalisation rates remain high, even at mid-term follow-up. This most probably results from the advanced clinical picture at time of referral for treatment. 相似文献
972.
P D Blanchard R A Angus R L Morrison S K Frost-Mason J H Sheetz 《Pigment cell research / sponsored by the European Society for Pigment Cell Research and the International Pigment Cell Society》1991,4(5-6):240-246
Electron micrographs of skin from xanthic (gold) sailfin mollies revealed numerous xanthophores, as well as scattered melanophores. The melanophores were seen to contain premelanosomes in various stages of development. This is consistent with the fact that xanthic mollies have been shown to be tyrosinase positive. Melanosomes in xanthic mollies appear to develop by one of two pathways: 1) from an endoplasmic reticulum-derived vesicle which develops an internal lamellar framework, and 2) by fusion of multiple Golgi-derived vesicles which lack an internal lamellar framework. Analysis of the pigments in the skin of the xanthic mollies identified four colorless pteridine pigments (xanthopterin, isoxanthopterin, neopterin, and pterin) and a carotenoid with an absorbance spectrum similar to beta-carotene. It appears that, unlike some other poeciliid fishes, sailfin mollies do not use pteridine pigments for orange coloration. Rather, they appear to rely primarily on carotenoids. 相似文献
973.
974.
975.
Gerald R.V. Hammond Matthias P. Machner Tamas Balla 《The Journal of cell biology》2014,205(1):113-126
Polyphosphoinositides are an important class of lipid that recruit specific effector proteins to organelle membranes. One member, phosphatidylinositol 4-phosphate (PtdIns4P) has been localized to Golgi membranes based on the distribution of lipid binding modules from PtdIns4P effector proteins. However, these probes may be biased by additional interactions with other Golgi-specific determinants. In this paper, we derive a new PtdIns4P biosensor using the PtdIns4P binding of SidM (P4M) domain of the secreted effector protein SidM from the bacterial pathogen Legionella pneumophila. PtdIns4P was necessary and sufficient for localization of P4M, which revealed pools of the lipid associated not only with the Golgi but also with the plasma membrane and Rab7-positive late endosomes/lysosomes. PtdIns4P distribution was determined by the localization and activities of both its anabolic and catabolic enzymes. Therefore, P4M reports a wider cellular distribution of PtdIns4P than previous probes and therefore will be valuable for dissecting the biological functions of PtdIns4P in its assorted membrane compartments. 相似文献
976.
977.
Sport hunting has reportedly multiple benefits to economies and local communities; however, few of these benefits have been quantified. As part of their lease agreements with the Zambia Wildlife Authority, sport hunting operators in Zambia are required to provide annually to local communities free of charge i.e., provision a percentage of the meat obtained through sport hunting. We characterized provisioning of game meat to rural communities by the sport hunting industry in Zambia for three game management areas (GMAs) during 2004–2011. Rural communities located within GMAs where sport hunting occurred received on average > 6,000 kgs per GMA of fresh game meat annually from hunting operators. To assess hunting industry compliance, we also compared the amount of meat expected as per the lease agreements versus observed amounts of meat provisioned from three GMAs during 2007–2009. In seven of eight annual comparisons of these GMAs, provisioning of meat exceeded what was required in the lease agreements. Provisioning occurred throughout the hunting season and peaked during the end of the dry season (September–October) coincident with when rural Zambians are most likely to encounter food shortages. We extrapolated our results across all GMAs and estimated 129,771 kgs of fresh game meat provisioned annually by the sport hunting industry to rural communities in Zambia at an approximate value for the meat alone of >US$600,000 exclusive of distribution costs. During the hunting moratorium (2013–2014), this supply of meat has halted, likely adversely affecting rural communities previously reliant on this food source. Proposed alternatives to sport hunting should consider protein provisioning in addition to other benefits (e.g., employment, community pledges, anti-poaching funds) that rural Zambian communities receive from the sport hunting industry. 相似文献
978.
N R Nuriddinova I A Lapaeva M V Guseva B Kh Vafakulov 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1990,(7):50-54
The test for the evaluation of the toxicity of different types of pertussis preparations as manifested by their in vitro influence on mouse thymic cells (T test) has been finally worked out. The use of the T test has made it possible to reveal the nonstandard character of the production lots of adsorbed diphtheria-pertussis-tetanus vaccines, both whole-cell vaccine and Japanese acellular vaccine. The degree of the in vitro damaging action of pertussis preparations on mouse thymic cells greatly depends on the residual content of Bordetella pertussis nontoxoidized toxin which, in contrast to B. pertussis lipopolysaccharide and filamentous hemagglutinin, produces pronounced cytotoxic action on mouse thymic cells. 相似文献
979.
OBJECTIVE: To determine the vaccination rate among infants discharged from a neonatal intensive care unit (NICU) and factors affecting that rate. DESIGN: Cross-sectional survey conducted when the children were 12 to 18 months of age. SETTING: NICU at the Royal University Hospital, Saskatoon, Sask. PARTICIPANTS: All 395 infants discharged from the NICU between Jan. 1 and June 30, 1992. MAIN OUTCOME MEASURES: Vaccination rate, ethnic background (native or non-native), place of residence (urban or rural), health status (number of days spent in the NICU), reasons for delay in or incomplete vaccinations (those involving parents'' responsibility, infant illness or contraindications). RESULTS: Of the 395 infants, 20 (5.0%) had died and incomplete information was available for 30 (7.6%). Complete data were available for 345 (87.3%). Of the infants for whom data were available, 8 (2.3%) had never been vaccinated and 142 (41.2%) had a delayed vaccination schedule or had not completed their scheduled vaccinations. Only 195 (56.6%) of the infants had received a full vaccination series. Non-native ethnic background was a predictor of completed vaccinations (odds ratio [OR] 5.40, 95% confidence interval [CI] 3.05 to 9.52). In a univariate model, urban area of residence was not a significant predictor of vaccination status, but when ethnic background was controlled for in a multivariate logistic regression analysis, urban area of residence was found to be inversely associated with completed vaccinations (OR 0.34, 95% CI 0.15 to 0.79). The number of days the child had spent in the NICU was not a significant predictor of vaccination status. CONCLUSION: The vaccination rate of infants discharged from the NICU is not optimal. Urban native children appears to be at risk of not being vaccinated. Non-native infants are five times more likely than native infants to have completed all of their scheduled vaccinations. Methods to improve the rate of completed vaccinations, especially for native children, must be sought and tested. 相似文献
980.
A sucrase gene from Leuconostoc mesenteroides was cloned and expressed in Escherichia coli. The cloned enzyme did not show dextransucrase or sucrose phosphorylase activity. HPLC and GC-MS analyses of the sucrase products indicated the presence of fructose and glucose in equimolar amounts. IPTG induction did not increase sucrase activity in E. coli indicating that the cloned gene may be transcribed from its own promoter. To our knowledge, this is the first sucrase cloned from L. mesenteroides that has invertase activity. 相似文献