全文获取类型
收费全文 | 4505篇 |
免费 | 242篇 |
国内免费 | 26篇 |
出版年
2024年 | 9篇 |
2023年 | 84篇 |
2022年 | 113篇 |
2021年 | 361篇 |
2020年 | 194篇 |
2019年 | 204篇 |
2018年 | 294篇 |
2017年 | 193篇 |
2016年 | 261篇 |
2015年 | 315篇 |
2014年 | 352篇 |
2013年 | 339篇 |
2012年 | 371篇 |
2011年 | 338篇 |
2010年 | 198篇 |
2009年 | 177篇 |
2008年 | 185篇 |
2007年 | 158篇 |
2006年 | 126篇 |
2005年 | 119篇 |
2004年 | 82篇 |
2003年 | 65篇 |
2002年 | 57篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有4773条查询结果,搜索用时 15 毫秒
961.
Xinyan Wu Muhammad Saddiq Zahari Santosh Renuse Nandini A. Sahasrabuddhe Min-Sik Kim Mary Jo Fackler Martha Stampfer Edward Gabrielson Saraswati Sukumar Akhilesh Pandey 《Clinical proteomics》2018,15(1):21
Background
Cancer-associated fibroblasts (CAFs) are one of the most important components of tumor stroma and play a key role in modulating tumor growth. However, a mechanistic understanding of how CAFs communicate with tumor cells to promote their proliferation and invasion is far from complete. A major reason for this is that most current techniques and model systems do not capture the complexity of signal transduction that occurs between CAFs and tumor cells.Methods
In this study, we employed a stable isotope labeling with amino acids in cell culture (SILAC) strategy to label invasive breast cancer cells, MDA-MB-231, and breast cancer patient-derived CAF cells. We used an antibody-based phosphotyrosine peptide enrichment method coupled to LC–MS/MS to catalog and quantify tyrosine phosphorylation-mediated signal transduction events induced by the bidirectional communication between patient-derived CAFs and tumor cells.Results
We discovered that distinct signaling events were activated in CAFs and in tumor epithelial cells during the crosstalk between these two cell types. We identified reciprocal activation of a number of receptor tyrosine kinases including EGFR, FGFR1 and EPHA2 induced by this bidirectional communication.Conclusions
Our study not only provides insights into the mechanisms of the interaction between CAFs and tumor cells, but the model system described here could be used as a prototype for analysis of intercellular communication in many different tumor microenvironments.962.
Ullah Habib Khan Adnan Daud Noman Muhammad Rehman Anees Ur 《Plasmonics (Norwell, Mass.)》2018,13(2):591-597
Plasmonics - We numerically analyzed a simple and novel design of multi-broadband plasmonic absorber which consists of a planar array of thin gold square ring structures on dielectric/metal... 相似文献
963.
Phase Boundary Derived Pseudocapacitance Enhanced Nickel‐Based Composites for Electrochemical Energy Storage Devices 下载免费PDF全文
Bei Long Muhammad‐Sadeeq Balogun Lei Luo Weitao Qiu Yang Luo Shuqin Song Yexiang Tong 《Liver Transplantation》2018,8(5)
Several strategies have been employed to improve the performance of energy storage devices through the development of new electrode materials. The construction of transition metal compound composite electrodes plays an important role in promoting the performance of energy storage devices. However, understandings of and insight into how to enhance the composites properties are rarely reported. Taking nickel‐based compounds as an example, Ni3N@Ni3S2 hybrid nanosheets are reported as a high‐performance anode material for lithium‐ion batteries that delivers higher lithium storage properties than the pristine Ni3N and Ni3S2 electrodes. This demonstrates that the phase boundaries between the Ni3N and Ni3S2 may contribute additional lithium storage, which leads to a synergistic effect via the high pseudocapacitance contribution from the outstanding conductivity of Ni3N and enhanced diffusion‐controlled capacity of Ni3S2. The use of composites prepared through sulfuration of hydrothermally annealed nickel hydroxide‐based precursor provides an enhancement of the energy storage properties. These results provide an important approach for increasing the electrochemical activity of composites by the combined effect of interfacial mismatch and pseudocapacitance, as well as understandings of the mechanism of the enhancement of the composite electrode properties. 相似文献
964.
Muhammad S. Haider Mahantesh M. Kurjogi Muhammad Khalil-ur-Rehman Tariq Pervez Jiu Songtao Muhammad Fiaz 《Journal of Plant Interactions》2018,13(1):83-90
It is indispensable to comprehend the mechanism that regulates plant responses to drought conditions to intensify the water use efficiency of stone fruits. The physiological, biochemical and molecular responses of drought-treated peach leaves were investigated. Results revealed that drought-treated plants manifested a significant attenuation in water potential as compared to control plants. Furthermore, sorbitol and proline contents were accumulated contrary to glucose, fructose, and sucrose that were dwindled significantly throughout the drought period. Similarly, the activities of antioxidant enzymes and expression pattern of related genes were hoisted to counter the lipid peroxidation in drought-treated plants. Moreover, reduced stomatal conductance has repressed the photosynthesis process and linked genes during drought stress. The expression level of regulatory genes (dehydration-responsive element-bindings and WRKYs) exhibited up-regulation in the drought-treated group. Overall, this study asserts that ‘Yoshihime’ peach cultivar possesses unique physiological, biochemical, and molecular responses under different spells of drought stress. 相似文献
965.
Gholib Gholib Muhammad Agil Iman Supriatna Bambang Purwantara Taufiq Purna Nugraha Antje Engelhardt 《Primates; journal of primatology》2018,59(3):281-292
Since the non-invasive field endocrinology techniques were developed, several fecal preservation and extraction methods have been established for a variety of species. However, direct adaptation of methods from previous studies for use in crested macaques should be taken with caution. We conducted an experiment to assess the accuracy and stability of fecal estrogen metabolite (E1C) and glucocorticoid metabolite (GCM) concentrations in response to several preservation parameters: (1) time lag between sample collection and fecal preservation; (2) long-term storage of fecal samples in 80% methanol (MeOH) at ambient temperature; (3) different degrees of feces drying temperature using a conventional oven; and (4) different fecal preservation techniques (i.e., freeze-drying, oven-drying, and field-friendly extraction method) and extraction solvents (methanol, ethanol, and commercial alcohol). The study used fecal samples collected from crested macaques (Macaca nigra) living in the Tangkoko Reserve, North Sulawesi, Indonesia. Samples were assayed using validated E1C and GCM enzyme immunoassays. Concentrations of E1C and GCM in unprocessed feces stored at ambient temperature remained stable for up to 8 h of storage after which concentrations of both E1C and GCM changed significantly compared to controls extracted at time 0. Long-term storage in 80% MeOH at ambient temperature affected hormone concentrations significantly with concentrations of both E1C and GCM increasing after 6 and 4 months of storage, respectively. Drying fecal samples using a conventional oven at 50, 70, and 90 °C did not affect the E1C concentrations, but led to a significant decline for GCM concentrations in samples dried at 90 °C. Different fecal preservation techniques and extraction solvents provided similar results for both E1C and GCM concentrations. Our results confirm previous studies that prior to application of fecal hormone analysis in a new species, several preservation parameters should be evaluated for their effects on hormone metabolite stability. The results also provide several options for fecal preservation, extraction, and storage methods that can be selected depending on the condition of the field site and laboratory. 相似文献
966.
Pamela H. Scott Nicola J. Veitch Helen Gadegaard Muhammad Mughal Gethin Norman Michelle Welsh 《Journal of biological education》2018,52(2):184-195
Laboratories are recognised as central in science education, allowing students to consolidate knowledge and master practical skills, however, their effectiveness has been questioned. Whilst laboratory practicals are useful for students’ learning of basic procedures, they have been shown to be less effective for developing conceptual understanding of the subject. Interactive lectures and bespoke digital resources were utilised in order to enhance theoretical understanding of laboratory practical molecular sessions, thus enabling students to take responsibility for and direct their own learning, encouraging inquiry-based learning. Providing easy to access additional learning resources offered students an opportunity to better prepare themselves for the laboratory, and consolidate their knowledge through subsequent review and self-testing in their own time. Grades before and after implementation of these active learning strategies were analysed to look at the impact on student learning and this study demonstrates that integrating these into a challenging practical biology course improved grades significantly with a concomitant increase in the number of ‘A’ grades attained. Feedback to evaluate use and perceptions of both interactive lectures and digital resources were also analysed. It has been shown here that these activities enhanced student experience and understanding of the course. 相似文献
967.
Spleen tyrosine kinase influences the early stages of multilineage differentiation of bone marrow stromal cell lines by regulating phospholipase C gamma activities 下载免费PDF全文
968.
969.
Morphological and mitochondrial DNA variation revealed an undescribed lineage under the genus Sperata (Bagridae) in Bangladesh 下载免费PDF全文
Mohammed Mahbub Iqbal M. M. Mahbub Alam Muhammad Anamul Kabir Snæbjörn Pálsson 《Acta zoologica》2018,99(2):177-187
Catfishes Sperata are popular, known for its taste and nutritional value, and are found naturally in wide variety of freshwaters in South Asia. The taxonomy of Sperata spp., sampled from Hakaluki Haor in Bangladesh, was re‐evaluated based on morphological variation and DNA barcoding. The collective variation in morphometric characters and mitochondrial DNA revealed an undescribed old and well‐separated lineage under the genus Sperata along with two previously known Sperata aor and Sperata seenghala in Bangladesh. Analyses of morphological traits suggested significant differentiation among Sperata species. The variation in mitochondrial DNA supported the distinct lineage and taxonomical discrimination. Sperata aor diverged earlier from the new lineage and Sperata seenghala with a divergence of 5.39 (CI: 3.91–7.19) Mya (PP > 90). Sperata seenghala and the new lineage shared a most recent common ancestry, which diverged from each other around 3.41 (CI: 2.24–4.62) Mya (PP > 90). Thus, the newly identified lineage could be a subspecies of S. seenghala or even a species under the genus Sperata. The information of the study will be useful for conservation, sustainable management and selective breeding of the putative species, including previously reported S. aor and S. seenghala in Bangladesh. 相似文献
970.
Lina Al Kury Vadym Sydorenko Manal M. A. Smail Muhammad Anwar Qureshi Anatoliy Shmygol Murat Oz Jaipaul Singh Frank Christopher Howarth 《Molecular and cellular biochemistry》2018,438(1-2):25-34
There is much evidence that a combination of ibuprofen (IBU) and Aspirin (ASA) can antagonize the irreversible inhibition of platelet function. This study was designed to investigate the degree of gastric damage, bleeding time (BT) and fluctuations in the serum levels of prostaglandin E2 (PGE2) and thromboxane A2 (TXA2) after oral administration of ASA (200 mg/kg) and IBU (50 mg/kg) either alone or in combination in rats in vivo. The stomach was assessed for any damage either after 6 h, 18 h or 6 days and carboxymethylcellulose (1% CMC) served as a vehicle and control. ELISA was used to measure TXA2 and PGE2 in serum. Bleeding time was assessed using tail blood. The results show that ASA and IBU either alone or in combination can cause gastric ulceration in 25–100% of the rats at 6 and 18 h. In contrast, gastric ulceration was seen in 50% of rats with a combination of ASA given before IBU only after 6 days of oral administration. BT was unaffected either by ASA or IBU when administered alone except after 18 h for IBU. In contrast, BT was significantly reduced when IBU was administered before ASA after 18 h and 6 days (P < 0.001). Serum PGE2 levels decreased significantly after ASA administered either alone or in combination with IBU for 6 h, 18 h and 6 days (P < 0.05). Serum TXA2 levels were significantly reduced after 6 h, 18 h and 6 days following ASA and IBU administration except for IBU alone which caused a significant increase in serum TXA2 6 days after its administration (P < 0.01). It can be concluded that ASA and IBU administered either alone or in combination can cause gastric ulcers in the rat stomach after 6 h and 18 h, but less severe after 6 days. IBU either alone or in combination with ASA reduced BT only after 18 h and 6 days of administration. Together, the results show that gastric ulceration correlated well with the inhibition of serum PGE2 and TXA2 levels. 相似文献