全文获取类型
收费全文 | 4283篇 |
免费 | 380篇 |
国内免费 | 377篇 |
专业分类
5040篇 |
出版年
2024年 | 8篇 |
2023年 | 60篇 |
2022年 | 138篇 |
2021年 | 251篇 |
2020年 | 160篇 |
2019年 | 200篇 |
2018年 | 183篇 |
2017年 | 140篇 |
2016年 | 221篇 |
2015年 | 268篇 |
2014年 | 289篇 |
2013年 | 319篇 |
2012年 | 381篇 |
2011年 | 336篇 |
2010年 | 204篇 |
2009年 | 180篇 |
2008年 | 220篇 |
2007年 | 169篇 |
2006年 | 176篇 |
2005年 | 152篇 |
2004年 | 146篇 |
2003年 | 114篇 |
2002年 | 117篇 |
2001年 | 100篇 |
2000年 | 86篇 |
1999年 | 79篇 |
1998年 | 48篇 |
1997年 | 44篇 |
1996年 | 40篇 |
1995年 | 35篇 |
1994年 | 28篇 |
1993年 | 21篇 |
1992年 | 20篇 |
1991年 | 23篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有5040条查询结果,搜索用时 0 毫秒
971.
Carola Ledderose Marco M. Hefti Yu Chen Yi Bao Thomas Seier Linglin Li Tobias Woehrle Jingping Zhang Wolfgang G. Junger 《Purinergic signalling》2016,12(4):673-685
In neutrophils, adenosine triphosphate (ATP) release and autocrine purinergic signaling regulate coordinated cell motility during chemotaxis. Here, we studied whether similar mechanisms regulate the motility of breast cancer cells. While neutrophils and benign human mammary epithelial cells (HMEC) form a single leading edge, MDA-MB-231 breast cancer cells possess multiple leading edges enriched with A3 adenosine receptors. Compared to HMEC, MDA-MB-231 cells overexpress the ectonucleotidases ENPP1 and CD73, which convert extracellular ATP released by the cells to adenosine that stimulates A3 receptors and promotes cell migration with frequent directional changes. However, exogenous adenosine added to breast cancer cells or the A3 receptor agonist IB-MECA dose-dependently arrested cell motility by simultaneous stimulation of multiple leading edges, doubling cell surface areas and significantly reducing migration velocity by up to 75 %. We conclude that MDA-MB-231 cells, HMEC, and neutrophils differ in the purinergic signaling mechanisms that regulate their motility patterns and that the subcellular distribution of A3 adenosine receptors in MDA-MB-231 breast cancer cells contributes to dysfunctional cell motility. These findings imply that purinergic signaling mechanisms may be potential therapeutic targets to interfere with the motility of breast cancer cells in order to reduce the spread of cancer cells and the risk of metastasis. 相似文献
972.
兰花鼠尾草(Salvia farinacea Benth.)两类腺毛发育过程中超微结构的研究 总被引:3,自引:0,他引:3
电镜观察表明:兰花鼠尾草(Salvia farinacea Benth.)的头状腺毛(capitate trichomes)和盾状腺毛(peltate trichomes)在超微结构方面存在明显不同,盾状腺毛的分泌细胞中占优势的细胞器是质体,而头状腺毛中是内质网和质体;成熟的盾状腺毛角质层下间隙明显,而头状腺毛不明显;盾状腺毛的柄细胞的侧壁出现完全的角质化现象,而头状腺毛则无;头状腺毛的基细胞液化程度比盾状腺毛的高。 相似文献
973.
Ying?Wu Rui?Wu Bangjiao?Zhang Tingting?Jiang Ning?Li Kai?Qian Bao?LiuEmail author Jian?ZhangEmail author 《Plant Growth Regulation》2012,66(2):137-143
Gardenia jasminoides Ellis is an evergreen tropical plant and favorite to gardeners throughout the world. Several studies have documented that
in vitro micropropagation can be used for clonal propagation of G. jasminoides Ellis, the efficiency remained low. In addition, no information is available on the genetic and epigenetic fidelity of the
micropropagated plants. Here, we report on a simplified protocol for high efficient micropropagation of G. jasminoides Ellis cv. “Kinberly” based on enhanced branching of shoot-tips as explants. The protocol consisted of sequential use of three
media, namely, bud-induction, elongation and root-induction. By using two molecular markers, amplified fragment length polymorphism
(AFLP) and methylation sensitive amplified polymorphism (MSAP), we analyzed the genetic and DNA methylation pattern stability
of 23 morphologically normal plants randomly taken from a sub-population (>100) of micropropagated plants originated from
a single shoot-tip. We found that of >1,000 scored AFLP bands across the 23 micropropagated plants, no incident of genetic
variation was detected. In contrast, of 750 scored MSAP bands, moderate but clear alteration in several DNA methylation patterns
occurred in the majority of the 23 micropropagated plants. The changed methylation patterns involved both CG and CHG sites
representing either hyper- or hypo-methylation, which occurred without altering the total methylation levels partly due to
concomitant hyper- and hypo-methylation alterations. Our results indicated that epigenetic instability in the form of DNA
methylation patterns can be susceptible to the in vitro micropropagation process for G. jasminoides Ellis, and needs to be taken into account in the process of large-scale commercial propagation of this plant. 相似文献
974.
Background
The application of 22-MHz high-frequency ultrasound allows for visualization of the inner part of the sural nerve. The aim of this study was to evaluate the morphological changes of sural nerves in patients with type 2 diabetes mellitus using ultrasound.Materials and Methods
The thickness/width (T/W) ratio, the cross-sectional area (CSA) of the sural nerves and the maximum thickness (MT) of the nerve fascicles were measured in 100 patients with type 2 diabetes mellitus and 50 healthy volunteers using 22-MHz ultrasound. Receiver operating characteristic (ROC) curves were plotted to determine the optimal cut-off values as well as the sensitivities and specificities. All parameters were significantly different between the subject and control groups. The ROC curves demonstrated that the MT was the most predictive of diabetic cutaneous neuropathy, with an optimal cut-off value of 0.365 mm that yielded a sensitivity of 90.3% and a specificity of 87.7%.Conclusions
The results of this study suggest that 22-MHz ultrasound may be a valuable tool for evaluating diabetic cutaneous nerve neuropathy. 相似文献975.
微量血胆红素测定仪的临床应用 总被引:4,自引:0,他引:4
目的 :了解微量血胆红素测定仪测定血胆红素的正确性。方法 :黄疸婴儿 5 0例 ,男 2 9例 ,女 2 1例 ,年龄平均为 2 1 6天。采用玻璃毛细管在患儿足跟采集少量血在微量血胆红素测定仪上测定 ,并与静脉采血测得的血胆红素值进行比较。结果 :二种方法测得的血红素值无显著差别 (P >0 0 5 ) ,二者之间有非常显著的相关 ,相关系数r=0 96 996 ,P <0 0 1。结论 :微量法测定血胆红素简便 ,迅速 ,减少对婴儿的损伤 ,为黄疸婴儿血胆红素的测定提供了较大方便 ,应予推广应用 相似文献
976.
Juan Jia Zhenjiao Cao Chengzhu Liu Zhenhua Zhang Li Lin Yiyun Wang Negar Haghipour Lukas Wacker Hongyan Bao Thorston Dittmar Myrna J. Simpson Huan Yang Thomas W. Crowther Timothy I. Eglinton Jin‐Sheng He Xiaojuan Feng 《Global Change Biology》2019,25(12):4383-4393
Subsoil contains more than half of soil organic carbon (SOC) globally and is conventionally assumed to be relatively unresponsive to warming compared to the topsoil. Here, we show substantial changes in carbon allocation and dynamics of the subsoil but not topsoil in the Qinghai‐Tibetan alpine grasslands over 5 years of warming. Specifically, warming enhanced the accumulation of newly synthesized (14C‐enriched) carbon in the subsoil slow‐cycling pool (silt‐clay fraction) but promoted the decomposition of plant‐derived lignin in the fast‐cycling pool (macroaggregates). These changes mirrored an accumulation of lipids and sugars at the expense of lignin in the warmed bulk subsoil, likely associated with shortened soil freezing period and a deepening root system. As warming is accompanied by deepening roots in a wide range of ecosystems, root‐driven accrual of slow‐cycling pool may represent an important and overlooked mechanism for a potential long‐term carbon sink at depth. Moreover, given the contrasting sensitivity of SOC dynamics at varied depths, warming studies focusing only on surface soils may vastly misrepresent shifts in ecosystem carbon storage under climate change. 相似文献
977.
将编码人 94个氨基酸的前列腺分泌蛋白 ( PSP94) c DNA与酵母整合载体 p PICZαA重组 ,构建的重组质粒线性化后转染酵母细胞 GS1 1 5,获得了 PSP94在酵母细胞中遗传性稳定表达酵母工程细胞 .诱导后的培养物中 ,rh PSP94表达量约为 0 .9mg/L,分子量约 1 6.5k D.培养上清经离子交换层析纯化后 ,目的蛋白的纯度为 92 % .体外在人前列腺癌细胞上活性分析表明 ,rh PSP94以1 0 0μg/L ,对该细胞的抑制率 2 0 .4% ;单纯新型 TNF,以 1 0 3 U/ml,抑制率 2 9.8% ;rh PSP94和新型 TNF以上述同样剂量联合应用 ,抑制率为 86.3% .提示 PSP94在体外对抗前列腺癌细胞有杀伤作用 ,但不明显 ;PSP94与新型 TNF联合应用 ,可使抑制率明显提高 ,可能 PSP94与新型 TNF有协同抗前列腺癌的作用 . 相似文献
978.
XiaoPeng Fu ShuHua Yang ManZhu Bao 《In vitro cellular & developmental biology. Plant》2008,44(3):194-202
In this study, we aimed to maximize the rates of somatic embryogenesis achievable in anther cultures of Chinese pink (Dianthus chinensis L.) (2n = 2x = 30). The genotype of the donor plant was found to be a major factor in determining the success rate. Conditions
imposed during anther culture (notably medium composition and light conditions) and pretreatments (namely, cold, heat, and
mannitol incubations) were also found to influence somatic embryo induction. For example, the highest levels of embryogenic
callus induction were achieved when the donor buds had been cold pretreated and the subsequent anther culture was maintained
in darkness. Furthermore, there appeared to be an interaction of genotype with culture conditions. Thus, in cultures of the
cultivar (cv.) ‘Carpet’, the highest rates of embryogenesis were obtained when the anthers had received a 5-d heat-shock,
but such a thermal treatment did not generally produce a significant effect. Likewise, a 3-d mannitol pretreatment was optimal
only for the cross-hybrid line ‘HC’. Assessment of the ploidy of the plants regenerated from the anther cultures revealed
both diploid and tetraploid plants. Histological and cytological observations showed that all of these (both from n-pollen
and 2n-pollen lines) derived from anther wall cells. Spontaneous chromosome doubling was inferred to have occurred during
the embryogenic callus culture period. 相似文献
979.
基于AFLP技术对中国虾夷扇贝群体种质资源的研究 总被引:4,自引:0,他引:4
利用AFLP技术对国内较具代表性的5个群体与日本群体虾夷扇贝相比照进行遗传多样性的分析.采用6对引物组合对6个群体178个个体进行扩增,共得到308个位点,6个群体的多态位点比例为62.66% ~69.81%,其中日本群体最高,小长山群体最低,且呈显著性差异;香农氏指数为0.337 ~0.374,其中日本群体最高,小长山群体最低.凌水桥群体与旅顺群体间遗传相似性最高(0.9810),小长山群体与凌水桥群体间遗传相似性最低(0.9641);相对的遗传距离的计算结果与遗传相似性结果一致.数据分析表明养殖方式对虾夷扇贝遗传多样性影响不大.本试验结果为我国虾夷扇贝种质遗传多样性维持、保护和可持续利用提供参考. 相似文献
980.
Wen Gao Ying Xu Jianxiang Liu Xiaolei Wang Xinhong Dong Guigen Teng Binbin Liu Jinpei Dong Chaoyi Ge Hui Ye Xuezhi Zhang Hong Cheng 《Helicobacter》2023,28(2):e12947