全文获取类型
收费全文 | 2620篇 |
免费 | 130篇 |
专业分类
2750篇 |
出版年
2023年 | 12篇 |
2022年 | 48篇 |
2021年 | 71篇 |
2020年 | 48篇 |
2019年 | 76篇 |
2018年 | 105篇 |
2017年 | 75篇 |
2016年 | 125篇 |
2015年 | 155篇 |
2014年 | 159篇 |
2013年 | 217篇 |
2012年 | 243篇 |
2011年 | 221篇 |
2010年 | 140篇 |
2009年 | 98篇 |
2008年 | 175篇 |
2007年 | 178篇 |
2006年 | 156篇 |
2005年 | 106篇 |
2004年 | 82篇 |
2003年 | 100篇 |
2002年 | 69篇 |
2001年 | 4篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有2750条查询结果,搜索用时 9 毫秒
171.
172.
173.
Nawrot-Porabka K Jaworek J Leja-Szpak A Szklarczyk J Macko M Kot M Mitis-Musioł M Konturek SJ Pawlik WW 《Regulatory peptides》2007,143(1-3):56-63
Ghrelin, a 28-amino-acid peptide produced predominantly by oxyntic mucosa has been reported to affect the pancreatic exocrine function but the mechanism of its secretory action is not clear. The effects of intraduodenal (i.d.) infusion of ghrelin on pancreatic amylase outputs under basal conditions and following the stimulation of pancreatic secretion with diversion of pancreato-biliary juice (DPBJ) as well as the role of vagal nerve, sensory fibers and CCK in this process were determined. Ghrelin given into the duodenum of healthy rats at doses of 1.0 or 10.0 microg/kg increased pancreatic amylase outputs under basal conditions or following the stimulation of pancreatic secretion with DPBJ. Bilateral vagotomy as well as capsaicin deactivation of sensory fibers completely abolished all stimulatory effects of luminal ghrelin on pancreatic exocrine function. Pretreatment with lorglumide, a CCK(1) receptor blocker, reversed the stimulation of amylase release produced by intraduodenal application of ghrelin. Intraduodenal ghrelin at doses of 1.0 or 10.0 microg/kg increased plasma concentrations of CCK and ghrelin. In conclusion, ghrelin given into the duodenum stimulates pancreatic enzyme secretion. Activation of vagal reflexes and CCK release as well as central mechanisms could be implicated in the stimulatory effect of luminal ghrelin on the pancreatic exocrine functions. 相似文献
174.
Cercariaeum crassum Wesenberg-Lund, 1934 is redescribed at the cercariaeum stage and the daughter-rediae and cercaria are also described on the basis of new material from Pisidium amnicum collected in the Liikasepuro River (eastern Finland). The species is allocated to the family Allocreadiidae, although its generic affiliation remains unknown. The probable life-cycle (based on the developmental stages observed in daughter-redia) appears to eliminate the cercarial stage and, instead, a cercariaeum (a type of cercaria without a tail) may develop directly from germ balls or, rarely, through the stages of an ophthalmoxiphidiocercaria that transforms into a young caudate cercariaeum. Their morphology and development are shown to be consistent with the family Allocreadiidae. The probable lack of a second intermediate host in the life-cycle is discussed. 相似文献
175.
Garbacz K Piechowicz L Haras K Wiśniewska K 《Medycyna do?wiadczalna i mikrobiologia》2007,59(3):195-200
The aim of this study was to examine whether Staphylococcus aureus of phage type 187 are genetically homogenous with the use of digestion of chromosomal DNA with SmaI and separation of the DNA by pulsed-field gel electrophoresis (PFGE). Sixteen S. aureus phage type 187 were isolated from the hospital patients (12) and the healthy carriers (4) in twelve medical centres in Poland during 1991 and 2005. The PFGE typing proved that the phage type 187 isolates have the same PFGE type (except for one) and constitute one clone. 相似文献
176.
Proteolysis of the membrane type-1 matrix metalloproteinase prodomain: implications for a two-step proteolytic processing and activation 总被引:1,自引:0,他引:1
Golubkov VS Chekanov AV Shiryaev SA Aleshin AE Ratnikov BI Gawlik K Radichev I Motamedchaboki K Smith JW Strongin AY 《The Journal of biological chemistry》2007,282(50):36283-36291
Membrane type-1 matrix metalloproteinase (MT1-MMP) exerts its enhanced activity in multiple cancer types. Understanding the activation process of MT1-MMP is essential for designing novel and effective cancer therapies. Like all of the other MMPs, MT1-MMP is synthesized as a zymogen, the latency of which is maintained by its inhibitory prodomain. Proteolytic processing of the prodomain transforms the zymogen into a catalytically active enzyme. A sequential, two-step activation process is normally required for MMPs. Our in silico modeling suggests that the prodomain of MT1-MMP exhibits a conserved three helix-bundled structure and a "bait" loop region linking helixes 1 and 2. We hypothesized and then confirmed that in addition to furin cleavage there is also a cleavage at the bait region in the activation process of MT1-MMP. A two-step sequential activation of MT1-MMP is likely to include the MMP-dependent cleavage at either P47GD downward arrowL50 or P58QS downward arrowL61 or at both sites of the bait region. This event results in the activation intermediate. The activation process is then completed by a proprotein convertase cleaving the inhibitory prodomain at the R108RKR111 downward arrowY112 site, where Tyr112 is the N-terminal residue of the mature MT1-MMP enzyme. Our findings suggest that the most efficient activation results from a two-step mechanism that eventually is required for the degradation of the inhibitory prodomain and the release of the activated, mature MT1-MMP enzyme. These findings shed more light on the functional role of the inhibitory prodomain and on the proteolytic control of MT1-MMP activation, a crucial process that may be differentially regulated in normal and cancer cells. 相似文献
177.
Beta-casomorphins, opioid peptides present in mother's milk, are a good substrate for DPPIV (EC 3.4.14.5) which is a major factor limiting the half-life of biologically active peptides. Serum DPPIV activity of two groups of infants (healthy and atopic dermatitis) and contents of beta-casomorphin-5 and -7 in their mothers' milk were determined in the study. We have found correlation between those two parameters in the group of children with atopic dermatitis syndromes, while no such a correlation was found in the control group. 相似文献
178.
Jarmołowska B Sidor K Iwan M Bielikowicz K Kaczmarski M Kostyra E Kostyra H 《Peptides》2007,28(10):1982-1986
Milk is the best, complete food important for the development and nourishment of a neonate. Except for nutrients, milk contains biologically active opioid peptides derived from beta-casein, named beta-casomorphins (BCMs), which can exert effects in the gastrointestinal tract as well as in the whole body of neonates. The content of beta-casomorphins in human milk during maturation phases has not been studied so far. The aim of this study was to determine the content of beta-casomorphin-5 and -7 in human milk in different phases of lactation. A significantly higher concentration of both beta-casomorphins was found in colostrum than in mature milk. The concentration of beta-casomorphin in milk collected in the second month of lactation was similar to the level obtained in the fourth month of lactation. The content of beta-casomorphins in human milk was observed with the period of lactation. The level of opioid peptides may depend on the function of these peptides in neonate's body and may be associated with the maturation process. 相似文献
179.
Epstein-Barr virus (EBV) infection in B-cell non-Hodgkin's lymphomas in children: virus latency and its correlation with CD21 and CD23 molecules 总被引:1,自引:0,他引:1
Kasprzak A Spachacz R Wachowiak J Stefanska K Zabel M 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》2007,45(3):169-179
Epstein Barr virus (EBV) infection of human B lymphocytes in vitro results in immortalisation of the cells and augmented membranous expression of numerous B-cell activation molecules, including CD23. Other studies demonstrated that only those B lymphocytes which carry the surface CD21 (EBV receptor) become transformation-competent. Inspired by the relatively unclear relations between expression of EBV and those of CD21 and CD23 in in vivo conditions we have decided to define correlations between tissue markers of EBV and of CD21 and CD23 molecules in B-cell non-Hodgkin's lymphomas (NHLs) in children. The studies were performed on an archival tissue material originating from children with B-cell NHLs (n=26) using immunocytochemical techniques, in situ hybridisation, and PCR. Our studies confirmed the latent phase of EBV infection in all of the EBV-positive patients. Viral proteins as well as viral RNAs (EBERs) was found both in the cytoplasm, in cell nuclei and in cell membranes of mainly the transformed lymphocytes B. Expression of the latent proteins (EBNA2 and LMP1) and that of EBERs in B-cell NHLs was significantly higher as compared to children with nonneoplastic lesions. The studies demonstrated reciprocally positive correlations between expressions of CD21 and CD23 in our children, but no correlation could be demonstrated between expression of EBV tissue markers and that of CD21 and/or CD23. Positive correlation was confirmed between expression of EBNA2 and LMP1 as well as between expression of the two proteins and EBERs in B-cell NHLs. Our studies have shown mainly latency III pattern of EBV. We have also demonstrated a novel form of EBV latency with no EBERs expression. The high detectability of EBV-positive cases both in the group of B-cell NHLs (77%), and in the group with non-neoplastic lesions (64%) suggested that only more pronounced tissue expression of EBV markers in B-cell NHLs as compared to the non-neoplastic material may point to a potential role of EBV in pathogenesis of lymphoma in this group of population in our country. 相似文献
180.
Interactive playback experiments were used to study the signal value to the corn bunting, Miliaria calandra, of alternating and overlapping singing. We subjected 15 males to two stimuli that differed in the temporal pattern of song
playback (alternating or overlapping). We measured eight characteristics of the males’ response in two categories—song output
and movements. Overlapping and alternating playback elicited a similar song response, characteristic of highly aroused males.
Song response correlated positively with males’ singing activity before playback, irrespective of stimulus. There were significant
differences between latency of approach to the loudspeaker and number of flights. Birds approached the loudspeaker more quickly
and spent more time close to it when playback alternated with their songs. The results suggest overlapping song could be interpreted
as a stronger threat but elicits a more cautious, rather than stronger, response than the alternating pattern. Males were
found to shorten songs during the playback compared with songs sung before and after stimulation. The only predictor of degree
of song shortening was song activity before the playback began. It should, therefore, be regarded as a signal which is related
to escalated, close-distance counter-singing. 相似文献