全文获取类型
收费全文 | 10308篇 |
免费 | 581篇 |
国内免费 | 32篇 |
专业分类
10921篇 |
出版年
2024年 | 26篇 |
2023年 | 114篇 |
2022年 | 356篇 |
2021年 | 542篇 |
2020年 | 330篇 |
2019年 | 421篇 |
2018年 | 452篇 |
2017年 | 327篇 |
2016年 | 468篇 |
2015年 | 530篇 |
2014年 | 633篇 |
2013年 | 797篇 |
2012年 | 844篇 |
2011年 | 726篇 |
2010年 | 440篇 |
2009年 | 354篇 |
2008年 | 443篇 |
2007年 | 443篇 |
2006年 | 389篇 |
2005年 | 384篇 |
2004年 | 298篇 |
2003年 | 252篇 |
2002年 | 227篇 |
2001年 | 110篇 |
2000年 | 98篇 |
1999年 | 80篇 |
1998年 | 60篇 |
1997年 | 31篇 |
1996年 | 36篇 |
1995年 | 41篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 47篇 |
1991年 | 42篇 |
1990年 | 46篇 |
1989年 | 42篇 |
1988年 | 44篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 37篇 |
1984年 | 33篇 |
1983年 | 27篇 |
1982年 | 21篇 |
1981年 | 26篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1977年 | 14篇 |
1976年 | 22篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
71.
Ali Riza Si?man Memduh Bülbül Canan Coker Banu Onvural 《Journal of trace elements in medicine and biology》2003,17(1):51-55
Cadmium is a nephrotoxic metal widely used in industry and the main source of Cd in general population is smoking. Considering that the source of Cd in cigarettes is the tobacco leaf, the exposure to Cd was evaluated in workers employed at a tobacco leaf processing factory. Blood and urinary Cd levels were measured by flameless atomic absorption spectrometry in 87 workers and 35 controls. Urinary enzymes, total protein, albumin and uric acid were also determined to investigate the possible nephrotoxic effects of Cd. Blood Cd levels were significantly higher in workers (1.63 +/- 1.95 microg/L) than in controls (0.91 +/- 1.15 microg/L) (p = 0.044). The increase observed in urinary Cd levels of workers was non significant (0.56 +/- 0.5 microg/g creatinine in workers and 0.46 +/- 0.5 microg/g creatinine in controls). Both in workers and in controls, subjects smoking >10 cigarettes/day showed significantly increased blood Cd levels compared to non-smokers (p = 0.000 and p = 0.011, respectively). In workers, urinary alkaline phosphatase (ALP), gamma glutamyl transferase (GGT), total protein, and uric acid were observed to be significantly increased (p = 0.013, p = 0.000, p = 0.000, p = 0.025, respectively), ALP, GGT and total protein being positively correlated with Cd in urine. In conclusion, the workers in the tobacco leaf processing factory were found to be exposed to Cd compared to the general population. The increase in the urinary enzymes and proteins suggests that an exposure to Cd affects kidney functions even below the toxic limits generally accepted. 相似文献
72.
73.
Background
Images of frozen hydrated [vitrified] virus particles were taken close-to-focus in an electron microscope containing structural signals at high spatial frequencies. These images had very low contrast due to the high levels of noise present in the image. The low contrast made particle selection, classification and orientation determination very difficult. The final purpose of the classification is to improve the signal-to-noise ratio of the particle representing the class, which is usually the average. In this paper, the proposed method is based on wavelet filtering and multi-resolution processing for the classification and reconstruction of this very noisy data. A multivariate statistical analysis (MSA) is used for this classification.Results
The MSA classification method is noise dependant. A set of 2600 projections from a 3D map of a herpes simplex virus -to which noise was added- was classified by MSA. The classification shows the power of wavelet filtering in enhancing the quality of class averages (used in 3D reconstruction) compared to Fourier band pass filtering. A 3D reconstruction of a recombinant virus (VP5-VP19C) is presented as an application of multi-resolution processing for classification and reconstruction.Conclusion
The wavelet filtering and multi-resolution processing method proposed in this paper offers a new way for processing very noisy images obtained from electron cryo-microscopes. The multi-resolution and filtering improves the speed and accuracy of classification, which is vital for the 3D reconstruction of biological objects. The VP5-VP19C recombinant virus reconstruction presented here is an example, which demonstrates the power of this method. Without this processing, it is not possible to get the correct 3D map of this virus.74.
We have studied the adsorption of atomic and molecular fluorines on a BC3 nanotube by using density functional calculations. It was found that the adsorption of atomic fluorine on a C atom of the tube surface is energetically more favorable than that on a B atom by about 0.97 eV. The adsorption of atomic fluorine on both C and B atoms significantly affects the electronic properties of the BC3 tube. The HOMO-LUMO energy gap is considerably reduced from 2.37 to 1.50 and 1.14 eV upon atomic F adsorption on B and C atoms, respectively. Molecular fluorine energetically tends to be dissociated on B atoms of the tube surface. The associative and dissociative adsorption energies of F2 were calculated to be about ?0.42 and ?4.79 eV, respectively. Electron emission density from BC3 nanotube surface will be increased upon both atomic and molecular fluorine adsorptions due to work function decrement. 相似文献
75.
Dai Yichen Cui Xiaolin Zhang Ge Mohsin Ali Xu Huiming Zhuang Yingping Guo Meijin 《Cytotechnology》2022,74(3):351-369
Cytotechnology - Human umbilical cord mesenchymal stem/stromal cells (hUC-MSCs) have attracted significant research interests in regenerative medicine and cell-based therapies due to their... 相似文献
76.
rafiei Ali Khodabakhsh Farnaz Cohan Reza Ahangari Azadegan-Dehkordi Fatemeh Salimian Morteza 《Molecular biology reports》2022,49(5):3389-3399
Molecular Biology Reports - Aberrant expression of long non-coding RNAs (lncRNAs) can contribute to the pathogenesis of coronary artery disease (CAD). In this study, we aimed to evaluate the... 相似文献
77.
Farrokhzad Yusuf Babaei Alireza Yadollahi Abbas Kashkooli Arman Beyraghdar Mokhtassi-Bidgoli Ali Hesami Shahriar 《Plant Cell, Tissue and Organ Culture》2022,149(3):535-548
Plant Cell, Tissue and Organ Culture (PCTOC) - We tested the feasibility to promote growth and shoot proliferation of Phalaenopsis through different wavelengths of LED and fluorescent. Therefore,... 相似文献
78.
Comparison of Th1 and Th2 responses in non-healing and healing patients with cutaneous leishmaniasis
Maryam Shahi Masoud Mohajery Seyyed Ali Akbar Shamsian Hossein Nahrevanian Seyyed Mohammad Javad Yazdanpanah 《Reports of Biochemistry & Molecular Biology》2013,1(2):43-48
Background:
Cutaneous leishmaniasis is an endemic disease in many regions of Iran, including the city of Mashhad. In recent years, some cases have not responded to Glucantime, the usual treatment for this disease. The cellular immune response caused by T-helper type 1 (Th1) cells has an important role in protection against leishmaniasis, and activation of the T-helper type 2 (Th2) response causes progression of the disease. By analyzing these responses we hope to find a more effective treatment than that currently in use for leishmaniasis patients.Methods:
The cellular immune responses in 60 cases of non-healing and healing cutaneous leishmaniasis, and individuals in a control group, were analyzed by measuring cytokines released by peripheral blood mononuclear cells (PBMCs) when stimulated with Leishmania major antigens by Enzyme Linked Immuno Sorbent Assay (ELISA).Results:
Subjects from the healing group secreted more interleukin-12 (IL-12) and interferon gamma (IFN-γ) (p<0.05) and less interleukins -4, -5, -10 (IL-4, IL-5, and IL-10) (p<0.005) and -18 (IL-18) (p=0.003) than the non-healing group.Conclusions:
The results demonstrate that secretion of cytokines that activate Th2 response including IL-4, IL-5 and IL-10 in non-healing subjects was higher than healing subjects and secretion of cytokines that activate Th1 response including IL-12 and IFN-γ in healing subjects was higher relative to the non-healing subjects. In this study it has been shown that the level of IL-18 progresses disease in non-healing patients when the level of IL-12 gets decreased. Key Words: Cytokines, Cutaneous leishmaniasis, Glucantime 相似文献79.
Mee Lee Looi Saiful Anuar Karsani Mariati Abdul Rahman Ahmad Zailani Hatta Mohd Dali Siti Aishah Md Ali Wan Zurinah Wan Ngah Yasmin Anum Mohd Yusof 《Journal of biosciences》2009,34(6):917-925
Although cervical cancer is preventable with early detection, it remains the second most common malignancy among women. An understanding of how proteins change in their expression during a particular diseased state such as cervical cancer will contribute to an understanding of how the disease develops and progresses. Potentially, it may also lead to the ability to predict the occurrence of the disease. With this in mind, we aimed to identify differentially expressed proteins in the plasma of cervical cancer patients. Plasma from control, cervical intraepithelial neoplasia (CIN) grade 3 and squamous cell carcinoma (SCC) stage IV subjects was resolved by two-dimensional gel electrophoresis and the resulting proteome profiles compared. Differentially expressed protein spots were then identified by mass spectrometry. Eighteen proteins were found to be differentially expressed in the plasma of CIN 3 and SCC stage IV samples when compared with that of controls. Competitive ELISA further validated the expression of cytokeratin 19 and tetranectin. Functional analyses of these differentially expressed proteins will provide further insight into their potential role(s) in cervical cancer-specific monitoring and therapeutics. 相似文献
80.
Shah HN Rajakaruna L Ball G Misra R Al-Shahib A Fang M Gharbia SE 《Systematic and applied microbiology》2011,34(1):81-86
Strains (n = 99) of Staphylococcus aureus isolated from a large number of clinical sources and tested for methicillin sensitivity were analysed by MALDI-TOF-MS using the Weak Cation Exchange (CM10) ProteinChip Array (designated SELDI-TOF-MS). The profile data generated was analysed using Artificial Neural Network (ANN) Analysis modelling techniques. Seven key ions identified by the ANNs that were predictive of MRSA and MSSA were validated by incorporation into a model. This model exhibited an area under the ROC curve value of 0.9147 indicating the potential application of this approach for rapidly characterising MRSA and MSSA isolates. Nearly all strains (n = 97) were correctly assigned to the correct group, with only two aberrant MSSA strains being misclassified. However, approximately 21% of the strains appeared to be in a process of transition as resistance to methicillin was being acquired. 相似文献