首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   636篇
  免费   41篇
林业   37篇
农学   16篇
  134篇
综合类   44篇
农作物   45篇
水产渔业   63篇
畜牧兽医   271篇
园艺   24篇
植物保护   43篇
  2024年   2篇
  2023年   11篇
  2022年   20篇
  2021年   44篇
  2020年   31篇
  2019年   41篇
  2018年   29篇
  2017年   23篇
  2016年   30篇
  2015年   21篇
  2014年   30篇
  2013年   34篇
  2012年   51篇
  2011年   59篇
  2010年   30篇
  2009年   28篇
  2008年   41篇
  2007年   37篇
  2006年   40篇
  2005年   24篇
  2004年   23篇
  2003年   9篇
  2002年   10篇
  2000年   4篇
  1998年   1篇
  1996年   1篇
  1994年   1篇
  1989年   1篇
  1988年   1篇
排序方式: 共有677条查询结果,搜索用时 15 毫秒
501.
502.
Canine oral malignant melanoma (COMM) is a potentially lethal cancer disease. We established primary cell lines from mostly amelanotic primary COMM and metastases and assessed lesions and derived cells for Melan A, PNL2 and CD146 expression. Then, migration and invasion of CD146‐enriched vs ‐depleted COMM cells were analysed. Epithelial‐to‐mesenchymal transition (EMT) was addressed by Vimentin‐staining and MMP2/MMP9 zymography. Phagocytic behaviour was analysed by histopathological examination and phagocytosis assay. While Melan A‐ and PNL2‐staining yielded inconsistent data, 100% of COMM sections and primary cells showed CD146 expression, suggesting that this protein may serve as a prognostic marker. An overall correlation between CD146‐expression and migration/invasion was not observed. All primary cell lines consistently expressed Vimentin and secreted biologically active MMP2, indicating that they had undergone EMT. Importantly, COMM sections exhibited cell‐in‐cell structures, and all primary cell lines exhibited phagocytic activity, supporting the concept that cell cannibalism may have a role in COMM progression.  相似文献   
503.
504.
Therapy of canine mammary tumours (CMTs) with classical antitumour drugs is problematic, so better therapeutic options are needed. Palbociclib (PD‐0332991) is an innovative and effective anticancer drug for the treatment of breast cancer in women. Palbociclib is an inhibitor of cyclin‐dependent kinase 4 (CDK4) and CDK6, which are key regulators of the cell cycle machinery and thus cell proliferation. In the present in vitro study, we investigated whether Palbociclib also represents a candidate drug to combat CMT. For this purpose, the effect of Palbociclib was analysed in P114 and CF41 cells, two CMT cell lines with an endogenous CDK4/6 co‐expression. Incubation of P114 and CF41 cells with Palbociclib resulted in a dose‐ and time‐dependent loss of phosphorylated retinoblastoma protein (pRb), a classical CDK4/6 substrate within the cell cycle machinery. Moreover, treatment of CMT cells with Palbociclib‐induced cell cycle arrest affected cell viability, prevented colony formation and impaired cell migration activity. Palbociclib also inhibited the growth of P114 and CF41 cell spheroids. Immunohistochemical analysis of canine patient samples revealed a consistent expression of CDK6 in different canine mammary carcinoma types, but an individual and tumour‐specific expression pattern of phosphorylated pRb independent of the tumour grade. Together, our findings let us suggest that Palbociclib has antitumour effects on CMT cells and that canine patients may represent potential candidates for treatment with this CDK4/6 inhibitor.  相似文献   
505.
506.
Climate warming is causing an advance of the latest spring frosts and a consequent decrease of spring freeze risk during flowering. Cultivation areas of early blooming tree crops, such as almond, could be shifted pole-ward as consequence of global warming. On the other hand, warming winters and springs can cause an advance of the flowering period. The aim of the present work was to estimate which was the impact of climate change in the past six decades on the spring freeze damage risk during the almond blooming period in the Abruzzo region of Italy. According to our analysis a reduction of spring freeze risk due to the mitigation of springtime temperatures was counterbalanced by advanced almond blooming leaving the risk of spring freeze damage unchanged. These results suggest that the adaptation of almond phenology to changing climates could continue to limit the northward expansion of almond in Italy. Finally, these results may suggest that the loss of suitable areas due to loss of chilling units in the warmest climate areas cannot be compensated for by a pole-ward shift of almond plantings.  相似文献   
507.

Context

Landscape ecology has traditionally been taught through theoretical classes or computer labs. On the other hand, field labs have been generally less used as a way of teaching landscape ecology concepts.

Objectives

We show that field labs with an inquiry-based approach, where students are involved in the investigation, are feasible for training students in landscape ecology. We evaluated how common field labs are in landscape ecology courses, and also their contribution for student learning.

Methods

We evaluated whether field labs are used in landscape ecology courses by scanning available syllabi. We also used outcomes from a course offered in Brazil to show how field labs can be integrated into landscape ecology courses.

Results

Only 18.2 % of the 44 syllabi we found had field labs. The case study developed in Brazil showed that field labs allowed students to develop important skills, including the ability to design field studies, choose appropriate scales of analysis, detect ecological patterns, and judge multiple hypotheses.

Conclusions

Field labs are still uncommon in landscape ecology courses, but they can be a useful tool to teach landscape ecology concepts and to help students developing the necessary skills to do research. We offer recommendations regarding how to incorporate field labs in landscape ecology courses.
  相似文献   
508.

Context

In modern agricultural landscapes, fragmentation of partial habitats is a significant filter for multi-habitat users, reducing local taxonomic and functional diversity. There is compelling evidence that small species are more susceptible than large species. The impact of habitat fragmentation on intraspecific body-size distribution, however, is yet unexplored.

Objectives

We tested habitat fragmentation, a major driver of pollinator loss, for its impact on intraspecific body-size distributions of solitary wild-bee species. Subsequently, we tested individual body size for its impact on pollination services.

Methods

We sampled 1272 individuals of the four most common Andrena wild bee species in 22 newly established flowering fields (0.21–0.41 ha) in Hessen, Central Germany, over two consecutive years. Study sites were located in a ca. 80 ha landscape context of increasing habitat fragmentation. We analysed the pollen loads of the most abundant species.

Results

Body size within local populations of the two medium-sized bees increased with fragmentation, suggesting intraspecific selection for higher dispersal capacity. Pollen analysis carried out for the most common species revealed that larger individuals visited a significantly smaller plant spectrum. Habitat fragmentation may thus alter pollination services without necessarily affecting species richness or composition.

Conclusions

Systematic body-size variation at the population level thus explains the considerable variability between simple community measures and ecosystem functioning. Filtering processes at the individual level require increased understanding for targeting pollination services under current and future land-use change.
  相似文献   
509.
OBJECTIVE: To identify prognostic factors in cats with injection-site sarcomas (ISSs). DESIGN: Retrospective case series. ANIMALS: 57 cats with ISSs. PROCEDURES: Medical records of cats were reviewed with regard to sex, age, anatomic site of tumor, tumor size, histologic grade, excision of a primary tumor versus excision of a recurrent ISS, use of excision alone versus excision plus adjuvant therapy, local tumor recurrence, and development of distant metastasis to predict overall survival time (ie, time from tumor excision to death). RESULTS: In univariate analyses, local recurrence and development of distant metastasis were significantly associated with survival time in cats. On multivariate analysis, development of distant metastasis remained a significant prognostic factor. Histologic grade was associated with distant metastasis, with cats having grade 3 tumors being significantly more likely to develop metastasis than cats with grade 1 and 2 tumors. Factors associated with local recurrence of ISSs were not identified. CONCLUSIONS AND CLINICAL RELEVANCE: The development of distant metastasis, which may occur later during the course of the disease, was identified as a prognostic factor for overall survival time in cats with ISSs. In addition, cats with histologic grade 3 ISSs should be considered for further interventional studies with chemotherapy to prevent the high rate of distant metastasis.  相似文献   
510.
Genetic variability and relationships among five cattle breeds (Holstein, Pinzgau, Limousin, Slovak Spotted and Charolais) bred in the Slovak Republic were investigated separately using 11 microsatellite markers and 61 blood group systems. Allele frequency, heterozygosity (Ho, HE) and PIC values were investigated. F-statistics were computed separately. For microsatellite markers FIS, FIT, FST and for blood groups HS, HT, GST parameters were calculated. Microsatellite and blood group comparison showed similar results by F-statistics but some differences were marked using the other methods. Both methods were able to detect close relation between Slovak Pinzgau and Slovak Spotted cattle breeds. Their relation was confirmed by genetic distance, principal component analysis (PCA) and coefficient of admixture (mY). Important divergences between different markers used in the study were observed by the characterisation of Limousin and Charolais breeds.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号