全文获取类型
收费全文 | 5638篇 |
免费 | 507篇 |
国内免费 | 466篇 |
专业分类
6611篇 |
出版年
2024年 | 12篇 |
2023年 | 88篇 |
2022年 | 200篇 |
2021年 | 329篇 |
2020年 | 214篇 |
2019年 | 246篇 |
2018年 | 278篇 |
2017年 | 185篇 |
2016年 | 212篇 |
2015年 | 371篇 |
2014年 | 377篇 |
2013年 | 470篇 |
2012年 | 540篇 |
2011年 | 480篇 |
2010年 | 256篇 |
2009年 | 253篇 |
2008年 | 284篇 |
2007年 | 260篇 |
2006年 | 196篇 |
2005年 | 182篇 |
2004年 | 139篇 |
2003年 | 141篇 |
2002年 | 111篇 |
2001年 | 122篇 |
2000年 | 87篇 |
1999年 | 106篇 |
1998年 | 60篇 |
1997年 | 47篇 |
1996年 | 41篇 |
1995年 | 47篇 |
1994年 | 36篇 |
1993年 | 25篇 |
1992年 | 40篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有6611条查询结果,搜索用时 15 毫秒
61.
作者编写《广东植物志》旋花科时,对据本科的花粉形态特征划分族和属的意义予肯定并采用之;现将其中4个属、6个分类单位的分类或其分布等予于报道.对华南和北越的心萼薯属植物作修订;论证本地区不产AniseiaChoisy.被认为该属的狭花心萼薯A.stenantho和大花心萼薯A.stenanthavar.macrosrephana均是龙骨萼牵牛Ipomoeaatenantha;心萼薯Aniseiabiflora是毛牵牛Aniseiasinensis;云南土丁桂Evolvulusyunnanensis作新异名处理.应为我国新纪录的归化种(美洲土丁桂E.nummularius);裂叶鳞蕊藤Lepistemonlobatum为越南新纪录.也分布于我国江西、海南;海滩牵牛Ipomoeostolonifera这个开白花的海滩植物是一种中草药;虎脚牵牛Ipomoeapes-tigridis是亚洲和非洲东部热带的广布种,广东大陆西部也有;它是IpomoeaLinn.选模式种;这属的中名,本文恢复《广州植物志》(1956)等采用的牵牛属,会比较确切用“番薯属”为这个属的中名。 相似文献
62.
"发酵工程实验"是生物工程专业的工程类重要主干课之一,是培养学生工程设计、工程实践和创新思维的重要课程。基于构思—设计—实现—运行(conceive—design—implement—operate,CDIO)理念,"发酵工程实验"通过构建模块化课程内容,以构思、设计、实现、运作的项目导向模块开展课程设计,进行目标导向的教学模式改革。以"发酵工程实验"课程为载体,将工程基础知识、发酵工程系统实践能力、团队合作能力、创新能力培养等融为一体。建立基于成果导向教育(outcome-based education,OBE)理念的学生学习效果评价体系,完成"发酵工程实验"课程教学任务。学生对改革后的"发酵工程实验"课程满意度明显提高,教学效果显著。 相似文献
63.
Yukun Xiao Meng Wang Haozhou Yang Haoran Qiu Haotian Lu Yumin Da Ganwen Chen Tianyuan Jiang Weiwei Fu Bihao Hu Junmei Chen Lei Chen Yishui Ding Baihua Cui Chonglai Jiang Zejun Sun Yu Long Haotian Yang Zhangliu Tian Lei Wang Wei Chen 《Liver Transplantation》2024,14(1):2302556
Electrocatalytic CO2 reduction (CO2R) coupled with renewable electricity has been considered as a promising route for the sustainability transition of energy and chemical industries. However, the unsatisfactory yield of desired products, particularly multicarbon (C2+) products, has hindered the implementation of this technology. This work describes a strategy to enhance the yield of C2+ product formation in CO2R by utilizing spatial confinement effects. The finite element simulation results suggest that increasing the number of shells in the catalyst wil lead to a high local concentration of *CO and promotes the formation of C2+ products. Inspired by this, Cu nanoparticles are synthesized with desired hollow multi-shell structures. The CO2 reduction results confirm that as the number of shells increase, the hollow multi-shell copper catalysts exhibit improved selectivity toward C2+ products. Specifically, the Cu catalyst with 4.4-shell achieved a high selectivity of over 80% toward C2+ at a current density of 900 mA cm−2. Evidence from in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy unveils that the multi-shell Cu catalyst exhibits an enhanced *COatop coverage and the stronger interaction with *COatop compared to commercial Cu, confirming the simulation results. Overall, the work promises an effective approach for boosting CO2R selectivity toward value-added chemicals. 相似文献
64.
65.
Yang Liu Yoshifumi Baba Takatsugu Ishimoto Xi Gu Jun Zhang Daichi Nomoto Kazuo Okadome Hideo Baba Peng Qiu 《International journal of biological sciences》2022,18(10):4101
The impact of the gut microbiome on host health is becoming increasingly recognized. To date, there is growing evidence that the complex characteristics of the microbial community play key roles as potential biomarkers and predictors of responses in cancer therapy. Many studies have shown that altered commensal bacteria lead to cancer susceptibility and progression in diverse pathways. In this review, we critically assess the data for gut microbiota related to gastrointestinal cancer, including esophageal, gastric, pancreatic, colorectal cancer, hepatocellular carcinoma and cholangiocarcinoma. Importantly, the underlying mechanisms of gut microbiota involved in cancer occurrence, prevention and treatment are elucidated. The purpose of this review is to provide novel insights for applying this understanding to the development of new therapeutic strategies in gastrointestinal cancer by targeting the microbial community. 相似文献
66.
Human bocavirus 1 (HBoV1), a member of the genus Bocaparvovirus of the family Parvoviridae, causes acute respiratory tract infections in young children. Well-differentiated pseudostratified human airway epithelium cultured at an air-liquid interface (HAE-ALI) is an ideal in vitro culture model to study HBoV1 infection. Unique to other parvoviruses, bocaparvoviruses express a small nonstructured protein NP1 of ~25 kDa from an open reading frame (ORF) in the center of the viral genome. NP1 plays an important role in viral DNA replication and pre-mRNA processing. In this study, we performed an affinity purification assay to identify HBoV1 NP1-inteacting proteins. We identified that Ku70 and RPA70 directly interact with the NP1 at a high binding affinity, characterized with an equilibrium dissociation constant (KD) of 95 nM and 122 nM, respectively. Furthermore, we mapped the key NP1-interacting domains of Ku70 at aa266-439 and of RPA70 at aa181-422. Following a dominant negative strategy, we revealed that the interactions of Ku70 and RPA70 with NP1 play a significant role in HBoV1 DNA replication not only in an in vitro viral DNA replication assay but also in HBoV1-infected HAE-ALI cultures. Collectively, our study revealed a novel mechanism by which HBoV1 NP1 enhances viral DNA replication through its direct interactions with Ku70 and RPA70. 相似文献
67.
【目的】构建高致病性2型猪链球菌05ZYH33菌株plcR基因敲除株,通过比较突变株与野生株生物学特性的差异,研究plcR基因在2型猪链球菌致病过程中的作用。【方法】利用同源重组技术敲除plcR基因,多重交叉PCR及RT-PCR鉴定并测序验证。比较野生株与突变株基本生物学特性的差异,小鼠攻毒实验分析plcR基因缺失对细菌毒力的影响。【结果】经RT-PCR证实05SSU0241与05SSU0242共转录,通过多重交叉PCR及RT-PCR证实成功构建plcR基因缺失突变株,基本生物学特性显示突变株的生长速率、菌落形态、溶血活性均无显著改变,小鼠致病性试验结果显示,野生株攻毒的小鼠死亡率为70%,突变株攻毒的小鼠死亡率为40%,毒力较野生株显著降低。【结论】plcR基因作为2型猪链球菌有毒株基因组中特有的外源基因,在细菌致病过程中具有重要作用。 相似文献
68.
69.
Jordan Bai Muhammad Farid Abdul-Rahman Anne Rifkin-Graboi Yap-Seng Chong Kenneth Kwek Seang-Mei Saw Keith M. Godfrey Peter D. Gluckman Marielle V. Fortier Michael J. Meaney Anqi Qiu 《PloS one》2012,7(10)
We studied a sample of 75 Chinese, 73 Malay, and 29 Indian healthy neonates taking part in a cohort study to examine potential differences in neonatal brain morphology and white matter microstructure as a function of ethnicity using both structural T2-weighted magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). We first examined the differences in global size and morphology of the brain among the three groups. We then constructed the T2-weighted MRI and DTI atlases and employed voxel-based analysis to investigate ethnic differences in morphological shape of the brain from the T2-weighted MRI, and white matter microstructure measured by fractional anisotropy derived from DTI. Compared with Malay neonates, the brains of Indian neonates’ tended to be more elongated in anterior and posterior axis relative to the superior-inferior axis of the brain even though the total brain volume was similar among the three groups. Although most anatomical regions of the brain were similar among Chinese, Malay, and Indian neonates, there were anatomical variations in the spinal-cerebellar and cortical-striatal-thalamic neural circuits among the three populations. The population-related brain regions highlighted in our study are key anatomical substrates associated with sensorimotor functions. 相似文献
70.
Jin Cui Xiaoqun Li Sicheng Wang Yiming Su Xiao Chen Liehu Cao Xin Zhi Zili Qiu Yao Wang Hao Jiang Biaotong Huang Fang Ji Jiacan Su 《Journal of cellular and molecular medicine》2020,24(11):6149-6161
Bone loss (osteopenia) is a common complication in human solid tumour. In addition, after surgical treatment of gynaecological tumour, osteoporosis often occurs due to the withdrawal of oestrogen. The major characteristic of osteoporosis is the low bone mass with micro-architectural deteriorated bone tissue. And the main cause is the overactivation of osteoclastogenesis, which is one of the most important therapeutic targets. Inflammation could induce the interaction of RANKL/RANK, which is the promoter of osteoclastogenesis. Triptolide is derived from the traditional Chinese herb lei gong teng, presented multiple biological effects, including anti-cancer, anti-inflammation and immunosuppression. We hypothesized that triptolide could inhibits osteoclastogenesis by suppressing inflammation activation. In this study, we confirmed that triptolide could suppress RANKL-induced osteoclastogenesis in bone marrow mononuclear cells (BMMCs) and RAW264.7 cells and inhibited the osteoclast bone resorption functions. PI3K-AKT-NFATc1 pathway is one of the most important downstream pathways of RANKL-induced osteogenesis. The experiments in vitro indicated that triptolide suppresses the activation of PI3K-AKT-NFATc1 pathway and the target point located at the upstream of AKT because both NFATc1 overexpression and AKT phosphorylation could ameliorate the triptolide suppression effects. The expression of MDM2 was elevated, which demonstrated the MDM-p53-induced cell death might contribute to the osteoclastogenesis suppression. Ovariectomy-induced bone loss and inflammation activation were also found to be ameliorated in the experiments in vivo. In summary, the new effect of anti-cancer drug triptolide was demonstrated to be anti-osteoclastogenesis, and we demonstrated triptolide might be a promising therapy for bone loss caused by tumour. 相似文献