首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5367篇
  免费   529篇
  5896篇
  2022年   42篇
  2021年   86篇
  2020年   52篇
  2019年   57篇
  2018年   60篇
  2017年   60篇
  2016年   128篇
  2015年   236篇
  2014年   253篇
  2013年   290篇
  2012年   411篇
  2011年   396篇
  2010年   237篇
  2009年   223篇
  2008年   335篇
  2007年   280篇
  2006年   285篇
  2005年   294篇
  2004年   291篇
  2003年   259篇
  2002年   288篇
  2001年   66篇
  2000年   47篇
  1999年   57篇
  1998年   74篇
  1997年   45篇
  1996年   48篇
  1995年   53篇
  1994年   53篇
  1993年   44篇
  1992年   35篇
  1991年   36篇
  1990年   49篇
  1989年   30篇
  1988年   32篇
  1987年   29篇
  1986年   30篇
  1985年   41篇
  1984年   46篇
  1983年   46篇
  1982年   35篇
  1981年   49篇
  1980年   41篇
  1979年   35篇
  1978年   27篇
  1977年   37篇
  1976年   29篇
  1974年   30篇
  1973年   28篇
  1972年   28篇
排序方式: 共有5896条查询结果,搜索用时 15 毫秒
981.
982.
We examined the effects of two microsporidian isolates of Nosema lymantriae (Germany isolate; Schweinfurt isolate) on the reproductive success of Lymantria dispar L. All possible mating combinations were tested. Both isolates affected the fecundity of infected females and the hatch of neonates. The infection of female L. dispar with either isolate resulted in a higher proportion of non-viable eggs; the survival of neonates during egg stage was not affected. When L. dispar larvae were infected with N. lymantriae [Germany] the number of eggs per egg mass decreased between 24 and 61%. When both adults were infected, the hatch rate decreased to 26%. While the infection of the male or the female host with the Germany isolate affected the number of eggs per egg mass and the hatch of progeny, we did not find a significant effect when male hosts were infected with the Schweinfurt isolate; only infection of the female L. dispar resulted in a reduction of the number of eggs per egg mass between 26 and 37%.  相似文献   
983.
Novel superabsorbent hydrogels were manufactured using chemically modified cashew gum (CGMA) and acrylamide (AAm) as reactants. The route for the synthesis was feasible due to the incorporation of glycidyl methacrylate (GMA) into structure of cashew gum (CG) to form the cashew gum-methacrylated (CGMA), in an appropriate mixture water-DMSO, as solvent, and using TEMED as catalyst. Thereafter, the CGMA was copolymerized with AAm yielding (CGMA-co-AAm) hydrogels. The main characteristics of raw and the modified materials are reported in this paper. 13C NMR, 1H NMR and FTIR spectroscopies confirmed the incorporation of vinyl groups, from GMA, into CG structure. By the spectrophotometry analyses, it was found that, ca. 82% of GMA was incorporated to the CG after 24 h of reaction. The cross-linking of CGMA or co-polymerization of CGMA with acrylamide leads to a hydrogel formation. Their gelation was characterized by FT-IR analysis. Alkaline hydrolysis at 40 °C for 3 and 4.5 h increased the water uptake (WU) capacity. Hydrolyzed CGMA-co-AAm hydrogels present higher values of WU (up to 1500) and may be classified as water superabsorbent material. Applications in agriculture, as soil conditioner, and in biomedical field, as biomaterial (scaffold) are being investigated.  相似文献   
984.
Streptococcus agalactiae or group B streptococcus (GBS) is the most common cause of neonatal sepsis and meningitis in neonates. One of the major questions is whether the GBS strains able to cause neonatal invasive disease have peculiar genetic features. A collection of S. agalactiae strains, isolated from cervix, vagina and rectum of 10 mothers and from throat, ear and umbilicus of their newborns was genetically characterized by pulsed-field gel electrophoresis (PFGE). This study demonstrated that the strains isolated from each mother and her child were all genetically identical but that the strains from the 10 mother/child pairs mutually were genetically heterogeneous and 10 different PFGE patterns were found. Although it has been suggested that PFGE would be able to identify virulence traits to direct decisions in antibiotic management, the heterogeneous feature of GBS strains does not support broad application.  相似文献   
985.
The structure of the peptide Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-OMe has been determined in crystals obtained from a dimethylsulfoxide–isopropanol mixture. Crystal parameters are as follows: C38H69N7O10 · H2O · 2C3H7OH, space group P21, a = 10.350 (2) Å, b = 26.084 (4) Å, c = 10.395(2) Å, β = 96.87(12), Z = 2, R = 8.7% for 2686 reflections observed > 3.0 σ (F). A single 5 → 1 hydrogen bond is observed at the N-terminus, while two 4 → 1 hydrogen bonds characteristic of a 310-helix are seen in the central segment. The C-terminus residues, Ala(6) and Leu(7) are expended, while Val(5) is considerably distorted from a helical conformation. Two isopropanol molecules make hydrogen bonds to the C-terminal segment, while a water molecule interacts with the N-terminus. The structure is in contrast to that obtained for the same peptide in crystals from methanol-water [ I. L. Karle, J. L. Flippen-Anderson, K. Uma, and P. Balaram (1990) Proteins: Structure, Function and Genetics, Vol. 7, pp. 62–73] in which two independent molecules reveal an almost perfect α-helix and a helix penetrated by a water molecule. A comparison of the three structures provides a snapshot of the progressive effects of solvation leading to helix unwinding. The fragility of the heptapeptide helix in solution is demonstrated by nmr studies in CDC13 and (CD3)2SO. A helical conformation is supported in the apolar solvent CDCl3, whereas almost complete unfolding is observed in the strongly solvating medium (CD3)2SO. © 1993 John Wiley & Sons, Inc.  相似文献   
986.
Capsule Some males brought building materials to nests and females who were paired with such males laid heavier clutches.  相似文献   
987.

Background

Hepatitis delta frequently leads to liver cirrhosis and hepatic decompensation. As treatment options are limited, there is a need for biomarkers to determine disease activity and to predict the risk of disease progression. We hypothesized that anti-HDV IgM could represent such a marker.

Methods

Samples of 120 HDV-infected patients recruited in an international multicenter treatment trial (HIDIT-2) were studied. Anti-HDV IgM testing was performed using ETI-DELTA-IGMK-2-assay (DiaSorin). In addition, fifty cytokines, chemokines and angiogenetic factors were measured using multiplex technology (Bio-Plex System). A second independent cohort of 78 patients was studied for the development of liver-related clinical endpoints (decompensation, HCC, liver transplantation or death; median follow up of 3.0 years, range 0.6–12).

Results

Anti-HDV IgM serum levels were negative in 18 (15%), low (OD<0.5) in 76 (63%), and high in 26 (22%) patients of the HIDIT-2 cohort. Anti-HDV IgM were significantly associated with histological inflammatory (p<0.01) and biochemical disease activity (ALT, AST p<0.01). HDV replication was independent from anti-HDV IgM, however, low HBV-DNA levels were observed in groups with higher anti-HDV IgM levels (p<0.01). While high IP-10 (CXCL10) levels were seen in greater groups of anti-HDV IgM levels, various other antiviral cytokines were negatively associated with anti-HDV IgM. Associations between anti-HDV IgM and ALT, AST, HBV-DNA were confirmed in the independent cohort. Clinical endpoints occurred in 26 anti-HDV IgM positive patients (39%) but in only one anti-HDV IgM negative individual (9%; p = 0.05).

Conclusions

Serum anti-HDV IgM is a robust, easy-to-apply and relatively cheap marker to determine disease activity in hepatitis delta which has prognostic implications. High anti-HDV IgM levels may indicate an activated interferon system but exhausted antiviral immunity.  相似文献   
988.
989.
In 223 cases of dogs presented to a specialist behavioural clinic in Brisbane, Australia, 87 (39%) were for severe aggression. The classes of aggression included dominance (31.6%), territorial (29%), predatory (12.3%), intermale (12.3%), sibling rivalry (7.9%), fear biting (6%) and idiopathic rage (0.9%). The breeds most represented which attacked humans were the Bull Terrier (16%), German Shepherd and crosses (15%), Cattle dog breeds (Blue Heeler and crosses, 9.2%), Terrier breeds (9.2%), Labrador (8%), Poodle and Cocker Spaniel (both 5.7%) and Rottweiler (4.6%). The dangerous dog list put out by the local Brisbane City Council includes the first three breeds mentioned and the Rottweiler as the top four breeds causing aggression problems.

Hospital records in Victoria and Queensland confirm that most damage is caused to humans by Bull Terriers and German Shepherds. Many breeds similar to those in our study are also represented in American data on aggressive breeds.

Treatments included obedience training only, restraint only, obedience and restraint, synthetic progestins and obedience, castration, progestins and obedience, castration and obedience, use of chlorpromazine and as a last resort, euthanasia (12.6%). Entire males formed the largest group (44%), followed by castrated males and females (both 21%) and spayed females (15%).

Several breeds (Boxer, Briand, Samoyed and St. Bernard) only attacked other animals and birds.

This study reinforces evidence that social disruption is caused by aggressive dogs, but it also indicates that many responsible clients seek advice on how to deal with this behavioural problem.  相似文献   

990.
Shen SH  Wertz DL  Klinman JP 《PloS one》2012,7(1):e29270
AOC3 is highly expressed in adipocytes and smooth muscle cells, but its function in these cells is currently unknown. The in vivo substrate(s) of AOC3 is/are also unknown, but could provide an invaluable clue to the enzyme's function. Expression of untagged, soluble human AOC3 in insect cells provides a relatively simple means of obtaining pure enzyme. Characterization of enzyme indicates a 6% titer for the active site 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor and corrected k(cat) values as high as 7 s(-1). Substrate kinetic profiling shows that the enzyme accepts a variety of primary amines with different chemical features, including nonphysiological branched-chain and aliphatic amines, with measured k(cat)/K(m) values between 10(2) and 10(4) M(-1) s(-1). K(m)(O(2)) approximates the partial pressure of oxygen found in the interstitial space. Comparison of the properties of purified murine to human enzyme indicates k(cat)/K(m) values that are within 3 to 4-fold, with the exception of methylamine and aminoacetone that are ca. 10-fold more active with human AOC3. With drug development efforts investigating AOC3 as an anti-inflammatory target, these studies suggest that caution is called for when screening the efficacy of inhibitors designed against human enzymes in non-transgenic mouse models. Differentiated murine 3T3-L1 adipocytes show a uniform distribution of AOC3 on the cell surface and whole cell K(m) values that are reasonably close to values measured using purified enzymes. The latter studies support a relevance of the kinetic parameters measured with isolated AOC3 variants to adipocyte function. From our studies, a number of possible substrates with relatively high k(cat)/K(m) have been discovered, including dopamine and cysteamine, which may implicate a role for adipocyte AOC3 in insulin-signaling and fatty acid metabolism, respectively. Finally, the demonstrated AOC3 turnover of primary amines that are non-native to human tissue suggests possible roles for the adipocyte enzyme in subcutaneous bacterial infiltration and obesity.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号