全文获取类型
收费全文 | 131500篇 |
免费 | 11364篇 |
国内免费 | 10492篇 |
出版年
2023年 | 1502篇 |
2022年 | 1834篇 |
2021年 | 5691篇 |
2020年 | 4375篇 |
2019年 | 5454篇 |
2018年 | 5182篇 |
2017年 | 3786篇 |
2016年 | 5435篇 |
2015年 | 8114篇 |
2014年 | 9499篇 |
2013年 | 10142篇 |
2012年 | 12253篇 |
2011年 | 11204篇 |
2010年 | 6901篇 |
2009年 | 6187篇 |
2008年 | 7225篇 |
2007年 | 6492篇 |
2006年 | 5741篇 |
2005年 | 4568篇 |
2004年 | 3979篇 |
2003年 | 3569篇 |
2002年 | 3082篇 |
2001年 | 2525篇 |
2000年 | 2299篇 |
1999年 | 2174篇 |
1998年 | 1276篇 |
1997年 | 1244篇 |
1996年 | 1175篇 |
1995年 | 1042篇 |
1994年 | 1025篇 |
1993年 | 777篇 |
1992年 | 1125篇 |
1991年 | 895篇 |
1990年 | 690篇 |
1989年 | 658篇 |
1988年 | 528篇 |
1987年 | 492篇 |
1986年 | 406篇 |
1985年 | 430篇 |
1984年 | 293篇 |
1983年 | 259篇 |
1982年 | 187篇 |
1981年 | 139篇 |
1980年 | 118篇 |
1979年 | 152篇 |
1978年 | 117篇 |
1977年 | 117篇 |
1975年 | 118篇 |
1974年 | 127篇 |
1973年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
An experiment was conducted to investigate the effect of phytase transgenic corn (PTC) on intestinal microflora, and the fate of transgenic DNA and protein in the digesta and tissues of broilers. A total of 160 1-day-old Arbor Acres commercial male broilers were randomly assigned to 20 cages (8 chicks per cage) with 10 cages (replicates) for each treatment. Birds were fed with a diet containing either PTC (54.0% during 1–21 days and 61.0% during 22–42 days) or non-transgenic isogenic control corn (CC) for a duration of 42 days. There were no significant differences (P>0.05) between birds fed with the PTC diets and those fed with the CC diets in the quantities of aerobic bacteria, anaerobic bacteria, colibacillus and lactobacilli, or microbial diversities in the contents of ileum and cecum. Transgenic phyA2 DNA was not detected, but phyA2 protein was detected in the digesta of duodenum and jejunum of broilers fed with the PTC diets. Both transgenic phyA2 DNA and protein fragments were not found in the digesta of the ileum and rectum, heart, liver, kidney, and breast or thigh muscles of broilers fed with the PTC diets. It was concluded that PTC had no adverse effect on the quantity and diversity of gut microorganisms; Transgenic phyA2 DNA or protein was rapidly degraded in the intestinal tract and was not transferred to the tissues of broilers. 相似文献
7.
The role of the epidermal growth factor-1 and hydrophobic stack domains of human factor IX in binding to endothelial cells. 总被引:6,自引:0,他引:6
W F Cheung D L Straight K J Smith S W Lin H R Roberts D W Stafford 《The Journal of biological chemistry》1991,266(14):8797-8800
To determine the function and specificity in factor IX of the first epidermal growth factor (EGF)-like domain and the eight-amino acid hydrophobic stack encoded by exon C (residues 39-46), these domains were replaced by the corresponding polypeptide regions of factor X and chimeric proteins were produced in human embryo kidney cells. Both chimeras were activated by factor XIa at a rate similar to plasma factor IX and exhibited calcium-dependent fluorescence quenching similar to plasma factor IX. Both chimeras competed equally for binding to the endothelial cell receptor. Our findings make it unlikely that the first EGF-like domain or the hydrophobic stack of factor IX are responsible for the specific binding of factor IX to its endothelial cell receptor. 相似文献
8.
1. Insect galls are abnormal plant growths that develop in response to a stimulus provided by a galling insect. The nutrition hypothesis suggests that the concentrations of nutritive compounds in galls are changed to provide optimum nutrition for the larvae and adults of galling insects. 2. To test the nutrition hypothesis, we determined the concentrations of 20 free amino acids in galls and in galled and ungalled twigs of Quercus fabri during the larval and adult stages of Andricus mukaigawae using high-performance liquid chromatography with ultraviolet–visible detection. 3. At the larval stage, the concentrations of 12 out of 20 amino acids in A. mukaigawae galls were significantly higher than those in galled and ungalled twigs. Asparagine and tryptophan were the most abundant nonessential and essential amino acids, respectively, in A. mukaigawae galls. 4. At the adult stage, the concentrations of most amino acids, except proline, were significantly lower in A. mukaigawae galls than in galled and ungalled twigs. The A. mukaigawae adults may not manipulate amino acid levels because the adults do not feed on galls. The decrease of amino acid levels in adult galls may be viewed as a depletion. 5. The composition of free amino acids in A. mukaigawae galls was significantly different from the composition in galled and ungalled twigs in both the larval and adult stages. 6. Our results may support the nutrition hypothesis. We suggest that a high concentration of proline in A. mukaigawae galls may protect larvae and adults from plant defense responses. 相似文献
9.
10.
A recursive least squares based on Multi-model is proposed for non-uniformly sampled-data nonlinear (NUSDN) systems. The corresponding state space model of an NUSDN system is derived using lifting technique. Taking advantage of the Fuzzy c-Mean Clustering algorithm, NUSDN is divided into several local models. The basic idea is that the NUSDN system is viewed as a model switching system under a given rule. Once the local models are identified, the global model is determined. A pH neutralization process validate the performance of the proposed algorithm. 相似文献