全文获取类型
收费全文 | 10875篇 |
免费 | 709篇 |
国内免费 | 1篇 |
专业分类
11585篇 |
出版年
2023年 | 66篇 |
2022年 | 130篇 |
2021年 | 225篇 |
2020年 | 150篇 |
2019年 | 183篇 |
2018年 | 265篇 |
2017年 | 216篇 |
2016年 | 335篇 |
2015年 | 548篇 |
2014年 | 517篇 |
2013年 | 791篇 |
2012年 | 866篇 |
2011年 | 800篇 |
2010年 | 547篇 |
2009年 | 475篇 |
2008年 | 623篇 |
2007年 | 597篇 |
2006年 | 598篇 |
2005年 | 533篇 |
2004年 | 500篇 |
2003年 | 478篇 |
2002年 | 450篇 |
2001年 | 91篇 |
2000年 | 90篇 |
1999年 | 91篇 |
1998年 | 111篇 |
1997年 | 104篇 |
1996年 | 66篇 |
1995年 | 90篇 |
1994年 | 76篇 |
1993年 | 66篇 |
1992年 | 64篇 |
1991年 | 74篇 |
1990年 | 56篇 |
1989年 | 48篇 |
1988年 | 45篇 |
1987年 | 41篇 |
1986年 | 26篇 |
1985年 | 39篇 |
1984年 | 59篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 49篇 |
1980年 | 37篇 |
1979年 | 33篇 |
1978年 | 30篇 |
1977年 | 24篇 |
1976年 | 20篇 |
1975年 | 26篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Two cases of trisomy 16 confined to placental tissue associated with an unfavourable outcome of the pregnancy are reported. In the first case, after a diagnosis of an apparent non-mosaic trisomy 16 at chorionic villi sample (CVS), an intrauterine fetal death occurred at the 22nd week. In the second case a mosaic with trisomy 16 was found in chorionic villi and the fetus was still-born at 38 weeks. From a comparison of their cases with those of the literature, the authors conclude that a trisomy 16 confined to placental tissue has a negative effect on fetal growth and pregnancy outcome. 相似文献
13.
Margarita Burguera-Pascu Alberto Rodríguez-Archilla Pilar Baca 《Journal of trace elements in medicine and biology》2007,21(2):92-101
The antimicrobial efficacy of zinc (Zn) salts (sulfate and acetate) against Streptococcus mutans (S. mutans) present in the oral cavity was tested in this study. The substantivity of Zn salts was assessed by determining the concentration of Zn in whole, unstimulated saliva and by measuring the magnitude of suppression of salivary S. mutans, 2h after rinsing. The concentration of Zn was measured by atomic absorption spectrometry (AAS) with electrothermal atomization (ET AAS) in saliva sampled before (basal) and 24h after mouth rinsing with different concentrations of Zn (0.1%, 0.5% and 1%) administrated as sulfate and acetate. The estimation of Zn levels in samples collected 30, 60, 90 and 120 min after rinsing was carried out by AAS with flame atomization (FAAS). Immediately after rinsing, the concentration of Zn in saliva sharply increased with respect to the baseline values (0.055+/-0.017 mg/L), followed by a sustained decrease, probably due to clearance of salivary flow or swallowing during sampling. A significant reduction (>87%) in the total mean S. mutans counts was found 2h after rinsing either with sulfate or acetate solutions, as evidence of the high substantivity and effectiveness of the Zn salts tested. A statistically significant inverse relationship (p<0.001 and the Pearson correlation coefficients between -34% and -50%) was found between Zn levels and the respective pH values measured in the samples collected 60 and 120 min after rinsing, sustaining the theory of bacterial glycolysis inhibition. 相似文献
14.
Ronald J.A. Wanders Carlo Van Roermund Cor Lof Alfred J. Meijer 《Analytical biochemistry》1983,129(1):80-87
A simple fluorimetric assay for the determination of carbamoyl phosphate in tissue extracts is described. In the assay, production of ATP from carbamoyl phosphate and ADP by carbamate kinase is coupled to the formation of NADPH, using glucose, hexokinase, NADP+, and glucose-6-phosphate dehydrogenase. Production of NADPH in this system proved to be equal to the amount of carbamoyl phosphate present. 相似文献
15.
Rocío García-Pérez Beatriz Revilla-Nuin Carlos M. Martínez Angel Bernabé-García Alberto Baroja Mazo Pascual Parrilla Paricio 《PloS one》2015,10(12)
Associated liver partition and portal vein ligation for staged hepatectomy (ALPPS) is a two-stage hepatectomy technique which can be associated with a hypertrophic stimulus on the future liver remnant (FLR) stronger than other techniques–such as portal vein ligation (PVL). However, the reason of such hypertrophy is still unclear, but it is suggested that liver transection combined with portal vein ligation (ALPPS) during the first stage of this technique may play a key role. The aim of this study is to compare the hypertrophic stimulus on the FLR and the clinical changes associated with both ALPPS and PVL in a rat surgical model. For this purpose, three groups of SD rats were used, namely ALPPS (n = 30), PVL (n = 30) and sham-treated (n = 30). The second stage of ALPPS (hepatectomy of the atrophic lobes), was performed at day 8. Blood and FLR samples were collected at 1, 24, 48 hours, 8 days and 12 weeks after the surgeries. ALPPS provoked a greater degree of hypertrophy of the FLR than the PVL at 48 hours and 8 days (p<0.05). The molecular pattern was also different, with the highest expression of IL-1β at 24h, IL-6 at 8 days, and HGF and TNF-α at 48 hours and 8 days (p<0.05). ALPPS also brought about a mild proliferative stimulus at 12 weeks, with a higher expression of HGF and TGF-β (p<0.05) than PVL. Clinically, ALPPS caused a significant liver damage during the first 48 hours, with a recovery of liver function at day 8. In conclusion, ALPPS seems to induce higher functional hypertrophy on the FLR than PVL at day 8. Such regenerative response seems to be leaded by a complex interaction between pro-mitogenic (IL-6, HGF, TNF-α) and antiproliferative (IL1-β and TGF-β) cytokines. 相似文献
16.
Distinct effects of climate warming on populations of silver fir (Abies alba) across Europe 下载免费PDF全文
17.
18.
Alberto Buson Alessandro Negro Luigi Grassato Massimo Tagliaro Marina Basaglia Claudio Grandi Angelo Fontana Marco P. Nuti 《FEMS microbiology letters》1996,145(1):55-62
Abstract A clone positive for d-carbamoylase activity (2.7 kb Hin dIII- Bam H1 DNA fragment) was obtained by screening a genomic library of Agrobacterium radiobacter in Escherichia coli . This DNA fragment contains an open reading frame of 912 bp which is predicted to encode a peptide of 304 amino acids with a calculated molecular mass of 34247 Da. The d-carbamoylase gene. named cauA , was placed under the control of T7 RNA-dependent promoter and expressed in E. coli BL21 (DE3). After induction with isopropyl-thio-β-d-galactopyranoside, the synthesis of d-carbamoylase in E. coli reached about 40% of the total protein. The expressed protein was shown to possess a molecular mass, on SDS-PAGE, of 36 kDa and showed an enhanced allowed us to establish that a Pro14 →Leu14 exchange leads to an inactive enzyme species, while a Cys279 →Ser279 exchange did not impair the functional properties of the enxyme. 相似文献
19.
20.