全文获取类型
收费全文 | 2087篇 |
免费 | 205篇 |
出版年
2021年 | 33篇 |
2020年 | 22篇 |
2019年 | 16篇 |
2018年 | 29篇 |
2017年 | 15篇 |
2016年 | 55篇 |
2015年 | 78篇 |
2014年 | 84篇 |
2013年 | 121篇 |
2012年 | 133篇 |
2011年 | 133篇 |
2010年 | 81篇 |
2009年 | 76篇 |
2008年 | 111篇 |
2007年 | 82篇 |
2006年 | 90篇 |
2005年 | 91篇 |
2004年 | 86篇 |
2003年 | 83篇 |
2002年 | 78篇 |
2001年 | 53篇 |
2000年 | 57篇 |
1999年 | 43篇 |
1998年 | 23篇 |
1997年 | 20篇 |
1996年 | 26篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 28篇 |
1992年 | 23篇 |
1991年 | 23篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 27篇 |
1987年 | 29篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 19篇 |
1983年 | 27篇 |
1981年 | 13篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 11篇 |
1975年 | 14篇 |
1974年 | 14篇 |
1973年 | 16篇 |
1972年 | 14篇 |
1971年 | 13篇 |
1968年 | 13篇 |
排序方式: 共有2292条查询结果,搜索用时 15 毫秒
181.
Naja Becher Merete Hein Carl C Danielsen Niels Uldbjerg 《Reproductive biology and endocrinology : RB&E》2010,8(1):113
Background
High concentrations of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have been identified in the cervical mucus plug (CMP) at term of pregnancy. Their physiological and pathophysiological implications, however, remain to be elucidated, and CMPs from preterm labor have never been examined. This study was therefore conducted to describe the concentrations of MMP-2, TIMP-1, MMP-8 and MMP-9 in the CMP in relation to gestational age, IL-8 as an indicator of inflammation, compartment of the CMP, and preterm labor. 相似文献182.
Viviana García Mir Jyrki Heinämäki Osmo Antikainen Niklas Sandler Ofelia Bilbao Revoredo Antonio Iraizoz Colarte Olga Maria Nieto Jouko Yliruusi 《AAPS PharmSciTech》2010,11(1):409-415
A “simplex-centroid mixture design” was used to study the direct-compression properties of binary and ternary mixtures of chitin and two cellulosic direct-compression diluents. Native milled and fractioned (125–250 μm) crustacean chitin of lobster origin was blended with microcrystalline cellulose, MCC (Avicel® PH 102) and spray-dried lactose–cellulose, SDLC Cellactose® (composed of a spray-dried mixture of alpha-lactose monohydrate 75% and cellulose powder 25%). An instrumented single-punch tablet machine was used for tablet compactions. The flowability of the powder mixtures composed of a high percentage of chitin and SDLC was clearly improved. The fractioned pure chitin powder was easily compressed into tablets by using a magnesium stearate level of 0.1% (w/w) but, as the die lubricant level was 0.5% (w/w), the tablet strength collapsed dramatically. The tablets compressed from the binary mixtures of MCC and SDLC exhibited elevated mechanical strengths (>100 N) independent of the die lubricant level applied. In conclusion, fractioned chitin of crustacean origin can be used as an abundant direct-compression co-diluent with the established cellulosic excipients to modify the mechanical strength and, consequently, the disintegration of the tablets. Chitin of crustacean origin, however, is a lubrication-sensitive material, and this should be taken into account in formulating direct-compression tablets of it. 相似文献
183.
Buris Christiansen Natalia Bellostas Muguerza Atheline Major Petersen Britt Kveiborg Christian Rask Madsen Hermann Thomas Nikolaj Ihlemann Jens Christian S?rensen Lars K?ber Hilmer S?rensen Christian Torp-Pedersen Helena Domínguez 《PloS one》2010,5(8)
Ingestion of glucosinolates has previously been reported to improve endothelial function in spontaneously hypertensive rats, possibly because of an increase in NO availability in the endothelium due to an attenuation of oxidative stress; in our study we tried to see if this also would be the case in humans suffering from essential hypertension.
Methods
40 hypertensive individuals without diabetes and with normal levels of cholesterol were examined. The participants were randomized either to ingest 10 g dried broccoli sprouts, a natural donor of glucosinolates with high in vitro antioxidative potential, for a 4 week period or to continue their ordinary diet and act as controls. Blood pressure, endothelial function measured by flow mediated dilation (FMD) and blood samples were obtained from the participants every other week and the content of glucosinolates was measured before and after the study. Measurements were blinded to treatment allocation.Results
In the interventional group overall FMD increased from 4% to 5.8% in the interventional group whereas in the control group FMD was stable (4% at baseline and 3.9% at the end of the study). The change in FMD in the interventional group was mainly due to a marked change in FMD in two participants while the other participants did not have marked changes in FMD. The observed differences were not statistically significant. Likewise significant changes in blood pressure or blood samples were not detected between or within groups. Diastolic blood pressure stayed essentially unchanged in both groups, while the systolic blood pressure showed a small non significant decrease (9 mm Hg) in the interventional group from a value of 153 mm Hg at start.Conclusion
Daily ingestion of 10 g dried broccoli sprouts does not improve endothelial function in the presence of hypertension in humans.Trial Registration
Clinicaltrials.gov NCT00252018相似文献184.
J S Christiansen P A Svendsen T Deckert 《Hormone and metabolic research. Supplement series》1979,(8):131-134
Nine insulin-dependent, juvenile-onset diabetics were treated for more than twenty four hours with an artificial beta cell (Biostator). Using the amounts and profile of the insulin delivered by the machine as a guide for subsequent subcutaneous therapy, a better state of control was obtained. However, with the algorithm constants used, we found the Biostator to deliver more insulin (average 36%) than needed for subcutaneous therapy. Repeated oral glucose tolerance tests show that constants used in the algorithms might be optimized. 相似文献
185.
C.A. Ramírez-Restrepo A. Pernthaner T.N. Barry N. López-Villalobos R.J. Shaw W.E. Pomroy W.R. Hein 《Animal Feed Science and Technology》2010,155(2-4):99-110
A 131-day rotational grazing experiment was conducted in the summer autumn of 2007/2008 to compare effects of feeding condensed tannin (CT)-containing willow (Salix spp.) fodder blocks (i.e., silvopastoral system) or perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) control pasture upon the immune response to gastrointestinal nematode parasite infection in Romney weaned lambs. Groups of lambs (n = 40) were allocated to either willow fodder blocks or control pasture; half of each group (n = 20) were regularly-drenched with anthelmintic at approximately 21 day intervals, whilst the remaining 20 weaned lambs were not drenched unless pre-determined faecal nematode egg counts (FEC) were reached, when all weaned lambs in that group were drenched with anthelmintic (i.e., trigger-drenching). Metabolizable energy and CT concentrations were higher in willow fodder versus pasture herbages. Weaned lambs grazing willow fodder blocks had lower live weight gain (92 g/day) and carcass weight (14.4 kg) than those grazing control pasture (134 g; 15.3 kg), with no effect of anthelmintic drenching. Regular anthelmintic treatment maintained similar and low FEC up to day 82, which then increased, whilst trigger-drenched lambs grazing willow fodder blocks had higher FEC than lambs grazing control pasture on three out of eight occasions. As judged by faecal larval cultures, grazing willow fodder blocks reduced the relative proportions of abomasal-dwelling parasites (Haemonchus contortus and Teladorsagia spp.). Trigger-drenched willow fodder block-fed sheep had higher platelet, eosinophil, total white blood cell and lymphocyte counts, greater CD21+ and greater γδ (Gamma Delta) TCR+ (T cell receptor) lymphocyte subsets than control pasture-fed sheep, and higher plasma levels of Immunoglobulin A (IgA) specific for carbohydrate larval antigen (CarLa) on day 105 (P<0.001). None of these parameters were affected by grazing treatment in regularly-drenched lambs. Higher immunological measurements in trigger-drenched lambs grazing willow fodder blocks could be due to higher larval intake and/or to the effects of secondary compounds in willow fodder blocks priming the immune system. Further research is required to separate these effects. 相似文献
186.
Ten specimens of the codfish Theragra finnmarchica(Teleostei, Gadidae) were known to science until 2003. Collections of 31 additional specimens made off north Norway between February 2003 and April 2004 provide information on the geographical and vertical distribution of this assumed rare species. 相似文献
187.
188.
Winter C Hein T Kavka G Mach RL Farnleitner AH 《Applied and environmental microbiology》2007,73(2):421-431
The Danube River is the second longest river in Europe, and its bacterial community composition has never been studied before over its entire length. In this study, bacterial community composition was determined by denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified portions of the bacterial 16S rRNA gene from a total of 98 stations on the Danube River (73 stations) and its major tributaries (25 stations), covering a distance of 2,581 km. Shifts in the bacterial community composition were related to changes in environmental conditions found by comparison with physicochemical parameters (e.g., temperature and concentration of nutrients) and the concentration of chlorophyll a (Chl a). In total, 43 distinct DGGE bands were detected. Sequencing of selected bands revealed that the phylotypes were associated with typical freshwater bacteria. Apparent bacterial richness in the Danube varied between 18 and 32 bands and correlated positively with the concentration of P-PO(4) (r = 0.56) and negatively with Chl a (r = -0.52). An artificial neural network-based model explained 90% of the variation of apparent bacterial richness using the concentrations of N-NO(2) and P-PO(4) and the distance to the Black Sea as input parameters. Between the cities of Budapest and Belgrade, apparent bacterial richness was significantly lower than that of other regions of the river, and Chl a showed a pronounced peak. Generally, the bacterial community composition developed gradually; however, an abrupt and clear shift was detected in the section of the phytoplankton bloom. Large impoundments did not have a discernible effect on the bacterial community of the water column. In conclusion, the riverine bacterial community was largely influenced by intrinsic factors. 相似文献
189.
Ethidium monoazide and propidium monoazide for elimination of unspecific DNA background in quantitative universal real-time PCR 总被引:1,自引:0,他引:1
Unspecific background DNA in quantitative universal real-time PCR utilizing a hydrolysis probe was completely suppressed by the addition of EMA or PMA to the PCR mix via cross-linking of the dyes to DNA during 650 W visible light exposure. The proposed procedure had no effect on the sensitivity of the real-time PCR reaction. 相似文献
190.
The production of arabinoxylan-degrading enzymes by the fungus Penicillium brasilianum, grown on different carbon and nitrogen sources as well as different environmental conditions was investigated. Highest feruloyl esterase (225 mU/ml) and alpha-L-arabinofuranosidase (211 mU/ml) activities were obtained when P. brasilianum was grown on sugar beet pulp, whereas maximum xylanase (17 U/ml) activity was found during growth on oat spelt xylan. Yeast extract was the preferable nitrogen source for the production of all the three enzymes. Further optimization of the production of the crude enzyme mixture was examined by experimental design using a D-optimal quadratic model. Investigation of the microbial regulation of enzyme production showed that the presence of free ferulic acid further stimulated the production and pointing to that the fungal regulatory mechanism involved a coordinated production and secretion of feruloyl esterase, xylanase and alpha-L-arabinofuranosidase. Since agroindustrial by-products are a potential source of phenolic acids, crude enzyme mixtures of P. brasilianum were tested for their hydrolysis abilities against eight complex or model substrates. While total release of phenolic acids and pentoses was not observed, the synergistic enhancement of hydrolysis in the presence of feruloyl esterase was clearly demonstrated. 相似文献